U.S.-Iran Tensions and Implications for U.S. Policy

Updated September 23, 2019 (R45795)
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Since May 2019, U.S.-Iran tensions have escalated significantly, but have stopped short of erupting into armed conflict. The Trump Administration, following its 2018 withdrawal from the 2015 multilateral nuclear agreement with Iran (Joint Comprehensive Plan of Action, JCPOA), has taken several steps in its campaign of applying "maximum pressure" on Iran. Iran and Iran-linked forces have attacked and seized commercial ships, caused destruction of some critical infrastructure in the Arab states of the Persian Gulf, and posed threats to U.S. forces and interests, including downing a U.S. unmanned aerial vehicle. Iran has exceeded some nuclear limitations stipulated in the JCPOA. The Administration has sent additional military assets to the region to try to deter future Iranian actions and has continued to impose additional U.S. sanctions on Iran.

President Donald Trump has said he wants a diplomatic solution that would not only ease tensions but resolve broader disputes with Iran, centered on a revised JCPOA that encompasses not only nuclear issues but also Iran's ballistic missile program and Iran's support for regional armed factions. High-ranking officials from several countries, including Japan, Germany, France, Oman, Qatar, and Iraq, as well as some Members of Congress, have sought to mediate to try to de-escalate U.S.-Iran tensions, or otherwise encourage direct talks between Iranian and U.S. leaders. President Trump has stated that he welcomes talks with Iranian President Hassan Rouhani without preconditions, but no direct talks have been known to take place to date or are scheduled, including during the upcoming U.N. General Assembly meetings in New York that both leaders are expected to attend.

The action-reaction dynamic between the United States and Iran has the potential to escalate into significant conflict. The United States military has the capability to undertake a large range of options against Iran, both against Iran directly and against its regional allies and proxies. However, Iran's alliances with and armed support for armed factions throughout the region, and its network of agents in Europe, Latin America, and elsewhere, give Iran the potential to expand confrontation into areas where U.S. response options might be limited. A September 14, 2019, attack on critical energy infrastructure in Saudi Arabia demonstrated that Iran and/or its allies have the capability to cause significant damage to U.S. allies and to U.S. regional and global economic and strategic interests, and raised questions about the effectiveness of U.S. defense relations with the Gulf states in preventing Iranian attacks.

Members of Congress have received additional information from the Administration about the causes of the uptick in U.S.-Iran tensions and Administration planning for further U.S. responses. They have responded in a number of ways; some Members have sought to pass legislation requiring congressional approval for any decision by the President to take military action against Iran.

Additional detail on U.S. policy options on Iran, Iran's regional and defense policy, and Iran sanctions can be found in CRS Report RL32048, Iran: Internal Politics and U.S. Policy and Options, by Kenneth Katzman; CRS Report RS20871, Iran Sanctions, by Kenneth Katzman; CRS Report R44017, Iran's Foreign and Defense Policies, by Kenneth Katzman; and CRS Report R43983, 2001 Authorization for Use of Military Force: Issues Concerning Its Continued Application, by Matthew C. Weed.

Context for Heightened U.S.-Iran Tensions

U.S.-Iran relations have been mostly adversarial—but with varying degrees of intensity—since the 1979 Islamic Revolution in Iran. Since then, U.S. officials consistently have identified Iran's support for militant Middle East groups as a significant threat to U.S. interests and allies. Attempting to constrain Iran's nuclear program took precedence in U.S. policy after 2002 as that program advanced. The United States also has sought to block Iran's ability to purchase advanced conventional weaponry and to develop ballistic missiles.

In May 2018, the Trump Administration withdrew the United States from the 2015 nuclear agreement (Joint Comprehensive Plan of Action, JCPOA), asserting that the accord did not address the broad range of U.S. concerns about Iranian behavior and would not permanently preclude Iran from developing a nuclear weapon.1 Administration officials, such as Secretary of State Michael Pompeo and his senior adviser on Iran affairs, Ambassador Brian Hook, say that Administration policy is to apply "maximum pressure" on Iran's economy to (1) compel it to renegotiate the JCPOA to address the broad range of U.S. concerns and (2) deny Iran the revenue to continue to develop its strategic capabilities or intervene throughout the region.2 Administration statements also suggest that an element of the policy could be to create enough economic difficulties to stoke unrest in Iran, possibly to the point where the regime collapses.3

As the Administration has pursued its policy of maximum pressure, bilateral tensions have escalated significantly, with U.S. steps going beyond the reimposition of all U.S. sanctions that were in force before JCPOA went into effect in January 2016. Key developments since April 2019 include the following:

Iranian Responses and Actions

Iran has been responding to the additional U.S. pressure in part by demonstrating its ability to harm global commerce and other U.S. interests and to raise new concerns about Iran's nuclear activities. Iran also could be trying to cause international actors, such as Russia, European countries, and countries in Asia that depend on stable oil supplies, to put pressure on the Trump Administration to reduce its sanctions pressure on Iran.

Attacks on Tankers

Actions by Iran's Regional Allies

In addition to direct Iranian action, Iran's allies in the region have been conducting attacks that might be linked to U.S.-Iran tensions, although it is not known definitively whether Iran directed or encouraged such attacks. Still, Trump Administration policy, as articulated by Secretary of State Pompeo, has been to hold Tehran responsible for the actions of its regional allies.13

Iran and U.S. Downings of Drones

On June 20, 2019, Iran shot down an unmanned aerial surveillance aircraft (RQ-4A Global Hawk Unmanned Aerial Vehicle) near the Strait of Hormuz, claiming it had entered Iranian airspace over the Gulf of Oman. U.S. Central Command officials stated that the drone was over international waters.20 IRGC commander-in-chief Major General Hossein Salami stated "The downing of the American drone is an open, clear and categorical message, which is: the defenders of the borders of Iran will decisively deal with any foreign aggression.... This is the way the Iranian nation deals with its enemies."

On June 20, 2019, according to his posts on the Twitter social media site, President Trump ordered a strike on three Iranian sites related to the Global Hawk downing, but called off the strike on the grounds that it would have caused Iranian casualties and therefore been "disproportionate" to the Iranian shootdown.21 The United States did reportedly launch a cyberattack against Iranian equipment used to track commercial ships.22

On July 18, 2019, President Trump announced that U.S. forces in the Gulf had downed an Iranian drone via electronic jamming in "defensive action" over the Strait of Hormuz. Iran denied that any of its drones were shot down.

UK-Iran Tensions and Iran Tanker Seizures

An effort by the United Kingdom (UK) to enforce EU sanctions against Syria opened up a dispute between Iran and the UK. On July 4, authorities from the British Overseas Territory Gibraltar, backed by British marines, impounded an Iranian tanker, the Grace I, off the coast of Gibraltar on the grounds that it was allegedly violating an EU embargo on the provision of oil to Syria. Iranian officials termed the seizure an illegitimate act of "piracy," and in subsequent days, the IRGC Navy sought to intercept a UK-owned tanker in the Gulf, the British Heritage, but the force was reportedly driven off by a British warship escorting the tanker. On July 19, the IRGC Navy seized a British-flagged tanker near the Strait of Hormuz, the Stena Impero, claiming variously that it violated Iranian waters, was polluting the Gulf, collided with an Iranian vessel, or that the seizure was retribution for the seizure of the Grace I.

On July 22, the UK's then-Foreign Secretary Jeremy Hunt explained the government's reaction to the Stena Impero seizure as pursuing diplomacy with Iran to peacefully resolve the dispute, while at the same time sending additional naval vessels to the Gulf to help secure UK commercial shipping there. Secretary Hunt stated that the UK had "made clear in public that [it] would be content with the release of Grace I if there were sufficient guarantees the oil would not go to any entities sanctioned by the EU."23 On August 15, following a reported pledge by Iran not to deliver the oil cargo to Syria, a Gibraltar court ordered the ship – which had been renamed the Adrian Darya 1 - released. Gibraltar courts turned down a U.S. Justice Department request to impound the ship as a violator of U.S. sanctions on Syria and on the IRGC, which the U.S. filing said was financially involved in the tanker and its cargo.24 The ship apparently, despite the pledge, delivered its oil to Syria,25 and, as a consequence, the United States imposed new sanctions on individuals and entities linked to the ship and to the IRGC-linked network that the Department of the Treasury identified as assisting that and other Iranian oil shipments. On September 22, 2019, Iran said the Stena Impero was now free to depart Iranian waters.

President Donald Trump and other senior U.S. officials publicly supported the UK position. Secretary of State Pompeo said that "the responsibility ... falls to the United Kingdom to take care of their ships."26 At the same time, UK officials stated that they remained committed to the JCPOA and would not join the Trump Administration campaign of maximum pressure on Iran.

Separate from the UK-Iran dispute over the Grace I and the Stena Impero, on August 5, Iran seized an Iraqi tanker for allegedly smuggling Iranian diesel fuel to "Persian Gulf Arab states."27

Parallels to Past Incidents in the Gulf28

Iran's apparent attacks on tankers in May and June share some characteristics with events in the mid-to-late 1980s during the 1980-1988 Iran-Iraq war. 1987-1988 represented the height of the so-called "tanker war," in which both Iran and Iraq were attacking ships in the Gulf. The United States backed Iraq during that war, and sought to limit and deter Iranian attacks on shipping, but there were several U.S.-Iran skirmishes in the Gulf. To protect commercial shipping, the United States launched "Operation Earnest Will" in July 1987, in which the United States reflagged 11 of Kuwait's oil tankers and the U.S. Navy escorted them through the Gulf. Almost immediately after the operation began, one of the tankers, the Bridgeton, was damaged by a large contact mine laid by Iran. In August 1987, U.S. forces captured the Iran Ajr, an Iranian landing craft being used for covert minelaying. However, Iran continued attacking, including with missiles; on October 16, 1987, an Iranian Silkworm missile struck on a U.S.-flagged Kuwaiti tanker, Sea Isle City, 10 miles off Kuwait's Al Ahmadi port. In response to that attack, U.S. destroyers and Special Operations forces blew up an Iranian oil platform east of Bahrain. On April 14, 1988, an Iranian-laid mine struck the U.S. frigate Samuel B. Roberts on patrol in the central Gulf, an attack that led to an April 16, 1988, naval confrontation in which the United States, in Operation Praying Mantis, put a large part of Iran's naval force out of action, including sinking one of Iran's two frigates and rendering the other inoperable. On July 3, 1988, mistaking it for an attacking Iranian aircraft, the guided missile cruiser USS Vincennes shot down Iran Air commercial passenger flight 655, killing all aboard.

Attack on Saudi Energy Infrastructure on September 1429

On September 14, an attack was conducted on multiple locations within critical Saudi energy infrastructure sites at Khurais and Abqaiq. The Houthi movement in Yemen, which receives arms and other support from Iran, claimed responsibility but Secretary of State Pompeo stated: "Amid all the calls for de-escalation, Iran has now launched an unprecedented attack on the world's energy supply. There is no evidence the attacks came from Yemen."30 Saudi officials said on September 16, 2019, that the attacks did not originate in Yemen and that the weapons used in the attack were of Iranian origin, but they did not name Iran as the perpetrator, instead inviting "U.N. and international experts ... to participate in the investigations."31 Press reports stated that U.S. intelligence indicates that Iran itself was the staging ground for the attacks, in which cruise missiles, possibly assisted by unmanned aerial vehicles, struck 17-19 targets at those Saudi sites.32 The Iraqi government denied that its territory was used for the strikes and said that Secretary Pompeo agreed in a call with Iraqi Prime Minister Adel Abd al Mahdi. Iranian officials have denied responsibility for the attack.

The attack shut down a significant portion of Saudi oil production and, whether conducted by Iran itself or by one of its regional allies, escalated U.S.-Iran and Iran-Saudi tensions and demonstrated a significant capability to threaten U.S. allies and interests. Whether, or how, the United States and/or Saudi Arabia or other countries might respond to the attack was not announced. President Trump wrote on Twitter: "There is reason to believe that we know the culprit, are locked and loaded depending on verification. But we are waiting to hear from the Kingdom as to who they believe was the cause of this attack, and under what terms we would proceed." Some critics, including some in Congress, expressed the view that President Trump was appearing to defer to Saudi Arabia too much decisionmaking input about the U.S. response to the attack.33 He also stated in a White House meeting on September 16 that he would "like to avoid" conflict with Iran, and it is possible that President Trump might be using apparent deference to Saudi Arabia to defray calls for a U.S. military response to the attack. Secretary of State Pompeo visited Saudi Arabia and the UAE during September 18-19 to discuss responses to the attack, and his press conferences in the region stated an intent to use diplomacy to try to resolve the crisis. U.S. officials also announced a modest increase in U.S. forces in the region and new U.S. sanctions. The issue is likely to form a major component of U.S. diplomacy during the U.N. General Assembly meetings the week of September 23.

The attacks on the Saudi infrastructure might raise broader questions about how to deal with Iran and the region, including:

JCPOA-Related Iranian Responses34

Since the Trump Administration's May 2018 announcement that the United States would no longer participate in the JCPOA, Iranian officials repeatedly have rejected renegotiating the agreement or discussing a new agreement. Tehran also has conditioned its ongoing adherence to the JCPOA on receiving the agreement's benefits from the remaining JCPOA parties, collectively known as the "P4+1." On May 10, 2018, Iranian Foreign Minister Mohammad Javad Zarif wrote that, in order for the agreement to survive, "the remaining JCPOA Participants and the international community need to fully ensure that Iran is compensated unconditionally through appropriate national, regional and global measures." He added that

Iran has decided to resort to the JCPOA mechanism [the Joint Commission established by the agreement] in good faith to find solutions in order to rectify the United States' multiple cases of significant non-performance and its unlawful withdrawal, and to determine whether and how the remaining JCPOA Participants and other economic partners can ensure the full benefits that the Iranian people are entitled to derive from this global diplomatic achievement.35

Tehran also threatened to reconstitute and resume the country's pre-JCPOA nuclear activities. According to Iranian officials, the country can rapidly reconstitute its fissile material production capability and has begun preparations for expanding its uranium enrichment program since the May 2018 U.S. announcement described above.36

Several meetings of the JCPOA-established Joint Commission since the U.S. withdrawal have not produced a firm Iranian commitment to the agreement.37 Tehran has argued that the remaining JCPOA participants' efforts have been inadequate to sustain the agreement's benefits for Iran. In May 8 letters to the other JCPOA participant governments, Iran announced that, as of that day, Tehran had stopped "some of its measures under the JCPOA," though the government emphasized that it was not withdrawing from the agreement. Specifically, Iranian officials said that the government will not transfer low enriched uranium (LEU) or heavy water out of the country in order to maintain those stockpiles below the JCPOA-mandated limits. A May 8 statement from Iran's Supreme National Security Council explained that Iran "does not anymore see itself committed to respecting" the JCPOA-mandated limits on LEU and heavy water stockpiles.38

Behrouz Kamalvandi, spokesperson for the Atomic Energy Organization of Iran (AEOI), warned on June 17, 2019, that Iran would exceed on June 27 the JCPOA-mandated quantitative limit on Iran's LEU stockpile if the agreement's other participants did not meet Tehran's demands. The Iranian government stated that it would resume full compliance with the JCPOA if the remaining participants agree during a 60-day period following the May 8, 2019, announcement to meet Tehran's demands (by July 7). However, Kamalvandi and other Iranian officials warned that, absent such an agreement, Iran would cease to accept any constraints on the concentration of Iranian-produced LEU. According to two July reports from then-IAEA Director General Yukiya Amano, both the quantity of Iran's LEU stockpile, as well as the that LEU's concentration of the relevant fissile isotope uranium-235, currently exceed JCPOA-mandated limits.39 A report from IAEA Acting Director General Cornel Feruță explains that Iran has continued this activity.40

Iranian officials have conditioned Tehran's continued implementation of its JCPOA commitments on fulfillment by France, Germany, and the United Kingdom (collectively known as the "E3") of Iran's demands described above. On August 27, Foreign Minister Zarif reportedly stated that Tehran will scale back still more of its JCPOA commitments, should the E3 fail to meet these demands.41 Deputy Foreign Minister Abbas Araqchi stated on August 28 that Iran's continued JCPOA participation depends on the government's ability to export oil or receive compensation for lost oil export revenue. Specifically, Araqchi explained, the E3 should persuade the United States to reinstate sanctions waivers that permitted such exports pursuant to the JCPOA. Should Washington refuse to do so, he argued, the E3 should "provide lines of credit" to Iran "equivalent to the amount of oil Iran would export."42 Some of these proposals are discussed further below.

Iranian President Hassan Rouhani Rouhani stated on September 5 that the AEOI

is required to start whatever technical needs of the country are in the field of research and development immediately, and put aside all [JCPOA-mandated] commitments in the field of research and development in all kinds of new centrifuges and everything we need for enrichment.43

Iran has begun installing advanced centrifuges at its pilot uranium enrichment facility, according to a September 8 report from Feruță.44 If Tehran and the P4+1 reach an agreement within 60 days, Iran will resume implementing its JCPOA commitments, Rouhani added in his September 5 statement.45 The remaining JCPOA participants apparently judge Tehran in compliance with the agreement.46

International Responses to the Current Dynamic

Responses by U.S. partners and others to the U.S.-Iran tensions have been consistent with the positions of major international players on the JCPOA. In general, U.S. partners and other countries have accepted U.S. charges of Iranian responsibility for the attacks on tankers and the September 14 strike on Saudi infrastructure. At the same time, however, U.S. partner countries have called for steps to de-escalate tensions and to avoid war in the region. For example, after the initial escalation of tensions in early May, Secretary of State Pompeo attended meetings with EU officials on May 13 to brief them on U.S. intelligence about the heightened Iranian threat. At the conclusion of the meetings, UK Foreign Secretary Jeremy Hunt stated "We [EU] are very worried about the risk of a conflict happening by accident, with an escalation unintended really on either side."47 The EU countries have said they will not, as a consequence of Iran's provocative acts, join the U.S. maximum pressure campaign. At the same time, some U.S. allies have joined a U.S. effort to deter Iran from further attacks on shipping in the Gulf. The U.S. efforts to construct a Gulf shipping protection operation are discussed further below.

Saudi Arabia, while avoiding directly blaming Tehran for the September 14 attacks, has called for an international response to them.

U.S. Responses

As tensions have increased with Iran, the Trump Administration has undertaken a number of steps to try to deter further attacks, weaken Iran strategically, and perhaps compel Iran to negotiate a broader resolution of U.S.-Iran differences.


Military Deployments

In response to the escalating tensions with Iran in recent months, the United States has added forces and military capabilities in the region, beyond the accelerated deployment of the USS Abraham Lincoln and associated forces, discussed above. The deployments have added several thousand U.S. military personnel to a baseline of more than 60,000 U.S. forces in and around the Persian Gulf, which include those stationed at military facilities in the Arab states of the Gulf Cooperation Council (GCC: Saudi Arabia, Kuwait, UAE, Qatar, Oman, and Bahrain), and those in Iraq and Afghanistan.50 Defense Department officials have indicated that the additional deployments since early May restore forces who were redeployed from the region a few years ago, and that the new deployments do not represent preparation for any U.S. offensive against Iran.51

Coalition to Secure the Gulf

The Trump Administration has sought to assemble a coalition that would use military assets to try to protect commercial shipping in the Gulf. In June, Secretary Pompeo visited Saudi Arabia, UAE, and several Asian states to recruit allies to contribute funds and military resources to a new maritime security and monitoring initiative (termed "Operation Sentinel") for the Gulf.56 The U.S. plan reportedly involves U.S. surveillance of Iranian naval movements and coordination of multilateral naval vessels escorting or protecting commercial ships under their respective flags. The U.S. plan appears to represent a version of the 1987-1988 "Operation Earnest Will," discussed in the textbox above.57At an August 28 press briefing, Defense Secretary Mark Esper told reporters "I am pleased to report that Operation Sentinel is up and running." The countries recruited to the mission are as follows:

Other nations, such as India, have sent some naval vessels to the Gulf to protect their commercial ships, and China's ambassador to the UAE said in early August that China is considering joining the mission, although no announcement of China's participation has since been made. Additionally, Israeli Foreign Minister Yisrael Katz said Israel would join the coalition, although it is likely that Israel would remain in a supporting role in light of the stated opposition of Iran, Iraq, and other regional governments to a direct Israeli military role in the Gulf.60 Defense Secretary Esper did not list Israel as a participant in his August 28 press briefing mentioned above. A question is whether additional countries might join the mission in the aftermath of the September 14 attack on Saudi critical infrastructure.

Scenarios and Possible Outcomes

Events could take any of several directions that might affect congressional oversight and authorization or limitations on the U.S. use of military force, Administration and congressional steps to support regional partners potentially affected by conflict, or new sanctions measures.

Further Escalation

U.S. and Iranian officials have said they do not want armed conflict. However, leaders on each side have said they will respond with force if the other attacks.

The Iranian leadership insists that U.S. sanctions be eased, and, in order to pressure on the United States to do so, Iran could undertake or provide material support for further actions such as the September 14 strike against Saudi critical energy infrastructure. Iran could potentially try to attack U.S. military, civilian, diplomatic, or other personnel. Iran could attack or seize additional commercial ships in the Gulf, possibly causing loss of life.

The IRGC's Qods Force (IRGC-QF) could encourage its allies in Syria, Lebanon,61 Iraq, Yemen, Bahrain, and Afghanistan to attack a wide range of targets, potentially including U.S. military personnel and installations.62 The IRGC-QF has supplied these regional allies with rockets, short-range ballistic missiles, and other weaponry to undertake such assaults.63 The annual State Department report on international terrorism has consistently asserted that Iran and its key ally, Lebanese Hezbollah, have a vast network of agents in Europe, Latin America, and elsewhere that could act against U.S. personnel and interests outside the Middle East.64 The U.S. intelligence community assess that Iran has "the largest inventory of ballistic missiles in the region," and press reports indicate that Iran is advancing its drone technology and the precision targeting of the missiles it provides to its regional allies. Israel asserts that these advances pose a sufficient threat to justify Israeli attacks against Hezbollah, additional targets in Syria, and apparently also against Iran-backed forces in Iraq during August 2019.65 The September 14 attack on Saudi critical energy infrastructure could represent an Iranian intent to escalate tensions, perhaps to increase pressure on the United States and its allies to ease sanctions.

Status Quo

It is possible that the U.S.-Iran tensions might not evolve to military conflict, but might not result in talks that lead to a potential resolution of the U.S.-Iran differences. At the August 28, 2019, DOD press briefing discussed above, Defense Secretary Esper asserted that the U.S.-led Gulf protection mission, Operation Sentinel, had "been successful" in deterring further Iranian attacks and that "I'm not sure I'm ready to call the crisis over yet, but so far so good. And we hope the trend lines continue that way." The September 14 attack appears to represent a break in that trend.


U.S. and Iranian officials have explored ways to de-escalate the tensions. Most experts assert that a compromise will require U.S. and/or EU efforts to ease pressure on Iran's economy, as well as Iran's acceptance of some additional limits beyond those stipulated in the JCPOA. President Trump and other senior officials have stated repeatedly since May 2019 that the United States is willing to talk directly with Iranian leaders, without preconditions, to de-escalate tensions and negotiate a revised JCPOA.66 For Iran's part, Foreign Minister Zarif visited the United Nations in July 2019 and offered, in return for the United States' lifting of U.S. JCPOA-related sanctions, to accelerate Iran's ratification of the Additional Protocol to its IAEA safeguards agreement ahead of the JCPOA-mandated schedule.67

Still, the United States and Iran do not have diplomatic relations and there have been no known high-level talks between Iran and the United States since the Trump Administration withdrew from the JCPOA. The absence of direct channels has led various third country leaders, as well as some Members of Congress, either with or separate from specific U.S. imprimatur, to try to move Tehran and Washington toward direct talks. Shortly after tensions began escalating, Secretary Pompeo had at least one direct contact with Sultan Qaboos of Oman, who in the past has mediated U.S.-Iran talks,68 and Japan's Prime Minister Shinzo Abe sought to mediate a de-escalation during his visit to Iran on June 12-13, 2019, the first visit to Iran by a Japanese leader since the Islamic revolution. That visit followed one by Germany's foreign minister to Tehran in early June. President Trump also confirmed on July 19, 2019, that he authorized Senator Rand Paul to engage in diplomatic discussions with Foreign Minister Zarif; Senator Paul reportedly met with Zarif in New York in July.69

Several Gulf countries, including Qatar and the UAE, have sent delegations to Iran to try to ease U.S.-Iran tensions that the Gulf leaders say could lead to severe destruction in the Gulf states themselves in the event of conflict.70 Whereas Qatar has consistently maintained relations with Iran, the UAE delegation that visited Tehran in late July undertook the first security talks with Iran since 2013 and their visit appeared to soften the country's position on engagement with Iran.

Prior to the September 14 attack on Saudi energy infrastructure, French President Macron appeared to produce some movement toward U.S.-Iran talks. In early July, he sent a top aide, Emmanuel Bonne, to Tehran for mediation talks. While hosting the G-7 summit in Biarritz, Macron invited Foreign Minister Zarif to meet with him and to speak with British and German diplomats. No Trump-Zarif meeting took place in Biarritz, and President Trump told reporters "I think it's too soon to meet, I didn't want to meet." However, at a press conference at the close of the summit, President Trump reiterated his willingness, in principle, to meet with Iranian President Hassan Rouhani, while at the same time reiterating his criticism of the JCPOA. President Macron expressed hope for a Trump-Rouhani meeting in the near future, presumably during the U.N. General Assembly meetings in New York in September. President Trump stated that he welcomes talks with Iranian President Hassan Rouhani without preconditions. Some press reports indicated that President Trump considered - possibly as an incentive for Iran to meet - supporting a French credit line proposal discussed below by approving sanctions waivers and exceptions to facilitate the credit line.71 However, in the wake of the September 14 attacks in Saudi Arabia, the Supreme Leader stated that there would be no U.S.-Iran talks and Rouhani and Zarif have restated the view that U.S. sanctions be lifted before any such talks. Yet, as the U.N. meetings got under way on September 23, President Trump still apparently did not rule out talks with Rouhani if the Iranian president were willing to undertake discussions.

Even if the United States and Iran do not talk directly, the EU or other actors could also produce a de-escalation by formulating policies that provide Iran with the economic benefits of the JCPOA. One new European proposal was revealed at the G-7 meeting: according to French officials, the proposal involves multiple countries providing a $15 billion credit line, secured by future deliveries of oil, in exchange for Iran's return to full JCPOA compliance. The credit line would be used to facilitate the operations of a new EU trading mechanism (Instrument in Support of Trading Exchanges, INSTEX) that has yet to complete any transactions.72

U.S. Military Action: Considerations, Additional Options, and Risks

The military is a tool of national power that the United States can use to advance its objectives, and the design of a military campaign and effective military options depend on the policy goals that U.S. leaders seek to accomplish. The Trump Administration has stated that its "core objective ... is the systemic change in the Islamic Republic's hostile and destabilizing actions, including blocking all paths to a nuclear weapon and exporting terrorism."73 As such, the military could be used in a variety of ways to try and contain and dissuade Iran from prosecuting its "hostile and destabilizing actions." These ways range from increasing presence and posture in the region to use of force to change Iran's regime. As with any use of the military instrument of national power, any employment of U.S. forces in this scenario could result in retaliatory Iranian action and/or the escalation of a crisis.

U.S. military action may not be the appropriate tool to achieve systemic change within the Iranian regime, and may in fact worsen the situation for Iranians sympathetic to a change of regime. Employing overt military force is likely to strengthen anti-American elements within the Iranian government. Some observers question the utility of military power against Iran due to global strategic considerations. The 2017 National Security Strategy and 2018 National Defense Strategy both note that China and Russia represent the key strategic challenges to the United States today and into the future. As such, shifting military assets into the United States Central Command (CENTCOM) area of responsibility requires diverting them from use in other theaters such as Europe and the Pacific, thereby sacrificing other long-term U.S. strategic priorities.

U.S. officials have stated that the additional U.S. deployments since May are intended to "deter" Iran from taking any further provocative actions. Yet, the downing of the RQ-4A Global Hawk Unmanned Aerial Vehicle on June 20, 2019, demonstrates that deploying additional assets and capabilities has not necessarily succeeded in deterring Iran from using military force.

Still others contend that the risks of military inaction are greater than those associated with the employment of force. For example, should Iran acquire a nuclear weapons capability, U.S. options to contain and dissuade it from prosecuting hostile activities could be significantly more constrained than they are at present.74

For illustrative purposes only, below are some potential additional policy options related to the possible use of military capabilities against Iran, beyond the Gulf shipping protection mission the United States is establishing. Not all of these options are mutually exclusive, nor do they represent a complete list of possible options, implications, and risks. And, the escalation of U.S.-Iran tensions has prompted Congress to assess its role in any decisions regarding whether to undertake military action against Iran, an issue that is discussed later in this report. The following discussion is based entirely on open-source materials.

Resource Implications of Military Operations

Without a more detailed articulation of how the military might be employed to accomplish U.S. objectives vis-a-vis Iran, and a reasonable level of confidence about how any conflict might proceed, it is difficult to assess with any precision the likely fiscal costs of a military campaign, or even just heightened presence. Still, any course of action listed in this report is likely to incur significant additional costs. Factors that might influence the level of expenditure required to conduct operations include, but are not limited to, the following:

Congressional Responses

Members of Congress have responded in various ways to increased tensions with Iran and to related questions of authorization for the use of military force.

Some Members have expressed concern about the legal justification for military operations in or against Iran. On June 22, Senator Bernie Sanders (I-VT) cast doubt on the notion of a "limited strike," saying that "[attacking] another country with bombs ... that's an act of warfare" and said that an attack on Iran would be, in his view, "unconstitutional."80 Although Presidents have long asserted wide-ranging authority to unilaterally initiate the use of military force, no legislation has been enacted authorizing the use of force against Iran, and several measures include provisions specifying that such authorization is not being granted.81 For instance, Section 9026 of Division C of H.R. 2740, as engrossed in the House on June 19, 2019, states that "Nothing in this Act may be construed as authorizing the use of force against Iran." H.R. 2500, the National Defense Authorization Act for FY2020, as reported in the House on June 19, 2019, contains a similar provision (Section 1225). On July 12, 2019, the House also passed, by a vote of 251-170, an amendment to H.R. 2500 that would prohibit funding for the use of force against Iran, with provisions clarifying that such a prohibition would not prevent the President from using necessary and appropriate force to defend U.S. allies and partners, consistent with the War Powers Resolution.

Other Members have positioned themselves as more generally supportive of broad discretion for the Administration to act. Senator Tom Cotton (R-AR) said on June 16 that "these unprovoked attacks on commercial shipping warrant a retaliatory military strike" and argued that the President had the authority to order such an attack.82 The day before, Senator Lindsey Graham (R-SC) made a similar argument, stating that "enough is enough" and called on President Trump to "be prepared to make Iran pay a heavy price by targeting their naval vessels and, if necessary, their oil refineries."83 On June 28, 2019, the Senate rejected by a 50-40 vote an amendment (S.Amdt. 883) to the FY2020 National Defense Authorization Act that would have prohibited the use of any funds to "conduct hostilities against the Government of Iran, against the Armed Forces of Iran, or in the territory of Iran, except pursuant to an Act or joint resolution of Congress specifically authorizing such hostilities."84

President Trump said in a June 24 interview that he believes he has the authority to direct strikes against Iran, and said that "I do like keeping them [Congress] abreast, but I don't have to do it, legally."85 On June 25, he tweeted that "any attack by Iran on anything American will be met with great and overwhelming force. In some areas, overwhelming will mean obliteration."86

At a Senate Foreign Relations Committee hearing on April 10, 2019, Secretary of State Pompeo, when asked if the Administration considers the use of force against Iran as authorized, answered that he would defer to Administration legal experts on that question. However, he suggested that the 2001 authorization for use of military force (AUMF, P.L. 107-40) against those responsible for the September 11 terrorist attacks could potentially apply to Iran, asserting that "[Iran has] hosted Al Qaida. They have permitted Al Qaida to transit their country. [There's] no doubt there is a connection between the Islamic Republic of Iran and Al Qaida. Period. Full stop." Other analyses have characterized the relationship between Iran and Al Qaeda as "an on-again, off-again marriage of convenience pockmarked by bouts of bitter acrimony."87 Section 9025 of H.R. 2740 would repeal the 2001 AUMF within 240 days of enactment.88

In a June 28, 2019, letter to House Foreign Affairs Committee Chairman Eliot Engel, Assistant Secretary of State for Legislative Affairs Mary Elizabeth Taylor stated that "the Administration has not, to date, interpreted either [the 2001 or 2002] AUMF as authorizing military force against Iran, except as may be necessary to defend U.S. or partner forces engaged in counterterrorism operations or operations to establish a stable, democratic Iraq." In response, Chairmen Engel and Middle East Subcommittee Chairman Ted Deutch welcomed the Administration's apparent acknowledgment that "the 2001 and 2002 war authorizations do not apply to military action against Iran," but cautioned that "the Administration claims that the President could use these authorizations to attack Iran in defense of any third party he designates a partner."89 In reviewing the letter, two analysts have suggested additional related topics for potential congressional oversight, including which groups are carrying out such counterterrorism operations, where they are doing so, and what nations or groups threaten them.90

Additionally, some Members seeking to prevent the Administration from pursuing military action against Iran have introduced several standalone measures prohibiting the use of funds for such operations, such as the Prevention of Unconstitutional War with Iran Act of 2019 (H.R. 2354/S. 1039) which would prevent the use of any funds for "kinetic military operations in or against Iran" except in case of an imminent threat.

Possible Issues for Congress

Given ongoing tensions with Iran, Members are likely to continue to assess and perhaps try to shape the congressional role in any decisions regarding whether to commit U.S. forces to potential hostilities. In assessing its authorities in this context, Congress might consider, among other things, the following:

Conflict with, or increased military activity in or around, Iran could generate significant financial costs. With that in mind, Congress could consider the following:

Figure 1. Iran, the Persian Gulf, and the Region

Sources: Created by CRS using data from the U.S. Department of State, ESRI, and GADM.

Appendix A. Selected Statements by U.S. and Iranian Leaders on Recent Tensions91

Date in 2019

U.S. Statements

Iranian Statements

April 22

Pompeo: "We have watched Iran have diminished power as a result of our campaign. Their capacity to wreak harm around the world is absolutely clearly diminished." 


April 24


FM Zarif: "It is not a crisis yet, but it is a dangerous situation. Accidents, plotted accidents are possible.... The plot is to push Iran into taking action. And then use that."

April 30


Rouhani: "America's decision that Iran's oil exports must reach zero is a wrong and mistaken decision, and we won't let this decision be executed and operational.... In future months, the Americans themselves will see that we will continue our oil exports."

May 5

National Security Advisor John Bolton statement: "In response to a number of troubling and escalatory indications and warnings, the United States is deploying the USS Abraham Lincoln Carrier Strike Group and a bomber task force to the U.S. Central Command region to send a clear and unmistakable message to the Iranian regime that any attack on United States interests or on those of our allies will be met with unrelenting force. The United States is not seeking war with the Iranian regime, but we are fully prepared to respond to any attack, whether by proxy, the Islamic Revolutionary Guard Corps, or regular Iranian forces."


May 8


President Rouhani (via Twitter): "Starting today, Iran does not keep its enriched uranium and produced heavy water limited. The EU/E3+2 will face Iran's further actions if they can not fulfill their obligations within the next 60 days and secure Iran's interests. Win-Win conditions will be accepted."

May 9

President Trump: "I'd like to see [Iran] call me" to "make a deal, a fair deal"


May 12


Rouhani: "The pressures by enemies is a war unprecedented in the history of our Islamic revolution ... but I do not despair and have great hope for the future and believe that we can move past these difficult conditions provided that we are united."

May 14


Supreme Leader Khamenei: "There won't be any war. The Iranian nation has chosen the path of resistance"

May 19

President Trump (via Twitter): "If Iran wants to fight, that will be the official end of Iran. Never threaten the United States again!"


May 20

President Trump (via Twitter): "Iran will call us if and when they are ever ready. In the meantime their economy continues to collapse—very sad for the Iranian people!"

Rouhani: "Today's situation is not suitable for talks and our choice is resistance only."

May 27

President Trump: "I really believe that Iran would like to make a deal, and I think that's very smart of them, and I think that's a possibility to happen.... It has a chance to be a great country with the same leadership.... We aren't looking for regime change—I just want to make that clear. We are looking for no nuclear weapons."


May 29

NSA Bolton: "I think it is clear these [tanker attacks] were naval mines almost certainly from Iran.... There is no doubt in anybody's mind in Washington who was responsible for this."

Supreme Leader Khamenei (via Twitter): "We won't negotiate with Americans. Because there's no use negotiating and it's even harmful. Otherwise we have no problems negotiating with others & with Europeans."

June 2

Pompeo: "We are prepared to engage in conversation with no preconditions, we are ready to sit down" with Iran.


June 13

President Trump (via Twitter): "While I very much appreciate [Japanese Prime Minister] Abe going to Iran to meet with Ayatollah Ali Khamenei, I personally feel it is too soon to even think about making a deal. They are not ready, and neither are we!"

Pompeo: "Iran is lashing out because the regime wants our successful maximum pressure campaign lifted.... Our policy remains an economic and diplomatic effort to bring Iran back to the negotiating table at the right time, to encourage a comprehensive deal that addresses the broad range of threats—threats today apparent for all the world to see—to peace and security."

Supreme Leader Khamenei (via Twitter): "We have no doubt in [PM Abe's] goodwill and seriousness; but regarding what you mentioned from U.S. president, I don't consider Trump as a person deserving to exchange messages with; I have no response for him & will not answer him."

June 17

President Trump, on alleged Iranian attacks in the Gulf: "So far, it's been very minor"


June 20

President Trump: "I find it hard to believe [Iran shooting down a U.S. drone] was intentional.... I have a feeling that it was a mistake made by somebody that shouldn't have been doing what they did."


June 21

President Trump: "I'm not looking for war, and if there is, it'll be obliteration like you've never seen before."


June 22

President Trump: "We're not going to have Iran have a nuclear weapon. And when they agree to that, they are going to have a wealthy country, they're going to be so happy and I'm going to be their best friend."


June 25

President Trump (via Twitter): "Iran's very ignorant and insulting statement, put out today, only shows that they do not understand reality. Any attack by Iran on anything American will be met with great and overwhelming force. In some areas, overwhelming will mean obliteration."

President Rouhani: "This White House is suffering from intellectual disability and doesn't know what to do"

July 14


President Rouhani: "We have always believed in talks ... if they lift sanctions, end the imposed economic pressure and return to the deal, we are ready to hold talks with America today, right now and anywhere"

August 8

President Trump (via Twitter): "Iran is in serious financial trouble. They want desperately to talk to the US, but are given mixed signals from all those purporting to represents us, including President Macron of France.... I know Emmanuel means well, as do all others, but nobody speaks for the United States but the United States itself."


August 26

President Trump: "The sanctions are absolutely hurting them horribly.... I don't want to see that. But we can't let them have a nuclear weapon.... So I think there is a really good chance we could meet [with Iran]."

President Rouhani: "If I knew that going to a meeting and visiting a person would help my country's development and resolve the problems of the people, I would not miss it.... We have to negotiate, we have to find a solution, we have to solve the problem."

August 27


Foreign Minister Zarif: "a meeting between the Iranian president and Trump is not imaginable until the U.S. returns to 5+1 and discharges [its commitments] under the JCPOA, and even then, there would be no bilateral talks."

September 16

At a meeting with the visiting Crown Prince of Bahrain, President Trump said: "Do I want war? I don't want war with anybody. I'm somebody that would like not to have war. We have the strongest military in the world. We've spent more than a trillion and a half dollars in the last short period of time on our military. Nobody has even come close. We have the best equipment in the world. We have the best missiles. And as you [Crown Prince] say, you just bought the Patriot system."


September 22

Secretary of State Pompeo: "President Trump and I both want to give diplomacy every opportunity to succeed. But I think the whole world knows that when that fails, when it's the case that we no longer believe that we can convince the Iranian regime to behave in the way that we've asked them to behave, just to behave like a normal nation, I think the whole world knows, including the Iranian regime, of American military might.


Figure A-1. Shipping Lanes in the Strait of Hormuz and Persian Gulf

Source: CRS. Based on, and includes, map by Navy of the United Kingdom.

Author Contact Information

Kenneth Katzman, Specialist in Middle Eastern Affairs ([email address scrubbed], [phone number scrubbed])
Kathleen J. McInnis, Specialist in International Security ([email address scrubbed], [phone number scrubbed])
Clayton Thomas, Analyst in Middle Eastern Affairs ([email address scrubbed], [phone number scrubbed])



For information on the JCPOA and the rationale for the U.S. withdrawal, see CRS Report R43333, Iran Nuclear Agreement and U.S. Exit, by Paul K. Kerr and Kenneth Katzman.


Speech by Secretary of State Michael Pompeo, Heritage Foundation, May 21, 2018; Testimony of Ambassador Brian Hook before the House Foreign Affairs Subcommittee on Middle East, North Africa, Hearing on U.S.-Iran Relations. June 19, 2019.


Speech by Secretary of State Pompeo, Heritage Foundation, op. cit.


Statement from the President on the Designation of the Islamic Revolutionary Guard Corps as a Foreign Terrorist Organization, April 8, 2019, at https://www.whitehouse.gov/briefings-statements/statement-president-designation-islamic-revolutionary-guard-corps-foreign-terrorist-organization/.


Department of State, Office of the Spokesperson, Factsheet: Designation of the Islamic Revolutionary Guard Corps, April 8, 2019.


State Department Factsheet, April 22, 2019, at https://www.state.gov/advancing-the-u-s-maximum-pressure-campaign-on-iran/.


Letter from Mary Elizabeth Taylor, Assistant Secretary of State for Legislative Affairs, to Senator James Risch, Chairman of the Senate Foreign Relations Committee. May 3, 2019.


The text of the announcement can be found at https://www.whitehouse.gov/briefings-statements/statement-national-security-advisor-ambassador-john-bolton-2/.


Letter from Secretary of State Michael R. Pompeo to Senate Foreign Relations Committee Chairman James E. Risch, May 24, 2019.


Department of Defense Briefing on Iran, May 24, 2019. For analysis on Saudi Arabia, see CRS Report RL33533, Saudi Arabia: Background and U.S. Relations, by Christopher M. Blanchard.


Pamela Falk, "Oil tanker attack probe reveals new photos, blames likely 'state actor,'" CBS News, June 7, 2019.


Statement by the Secretary of State, June 13, 2019.


Pompeo Warns Iran about Trigger for U.S. Military Action as Some in Administration Question Aggressive Policy. Washington Post, June 18, 2019.


For analysis on Iraq, see CRS Report R45025, Iraq: Background and U.S. Policy, by Christopher M. Blanchard.


Department of Defense Briefing on Iran. May 24, 2019, op. cit.


"Rockets strike near U.S.-linked oil installation and military bases in Iraq; 3 wounded," Washington Post, June 19, 2019.


"U.S. says Saudi pipeline attacks originated in Iraq: Wall Street Journal," Reuters, June 28, 2019. For analysis on the Yemen conflict, see CRS Report R43960, Yemen: Civil War and Regional Intervention, by Jeremy M. Sharp.


Sadursan Raghavan, "Yemeni rebels claim new drone attack on Saudi airport," Washington Post, June 17, 2019.


"The Taliban Claimed an Attack on U.S. Forces. Pompeo Blamed Iran," Washington Post, June 16, 2019.


See U.S. Central Command Statement at https://www.centcom.mil/MEDIA/STATEMENTS/Statements-View/Article/1881682/us-central-command-statement-iranians-shoot-down-us-drone/.


President Donald Trump interview on "Meet the Press," June 23, 2019.


"U.S. Cyberattack made it Harder for Iran to Target Oil Tankers." New York Times, August 29, 2019.


UK Foreign and Commonwealth Office, Statement by Jeremy Hunt to Parliament, July 22, 2019.


"Iran Warns U.S. Against Seizing Oil Tanker Headed to Greece." Bloomberg, August 18, 2019.


Iran Tanker Unloaded its Cargo, Tehran Says. New York Times, September 10, 2019.


"In naval confrontation with Iran, great Britain can find neither ships nor friends," Defense News, July 25, 2019.


"Iran Reportedly Seizes Iraqi Tanker In Persian Gulf." NPR, August 5, 2019.


Much of this textbox is derived from Ronald O'Rourke, U.S. Naval Institute Proceedings, "The Tanker War," May 1988; and CRS Issue Brief IB87145, "Persian Gulf: U.S. Military Operations," January 19, 1989.


For more detail on the attacks and implications, see: CRS Insight IN11167, Attacks Against Saudi Oil Rattle Markets, by Michael Ratner, Christopher M. Blanchard, and Heather L. Greenley and CRS Report RL33533, Saudi Arabia: Background and U.S. Relations, by Christopher M. Blanchard.


Secretary Pompeo on Twitter. 3:59 PM, September 14, 2019.


Kingdom of Saudi Arabia Ministry of Foreign Affairs Statement. September 16, 2019.


U.S. Tells Saudi Arabia Oil Attacks Were Launched from Iran." Wall Street Journal, September 16, 2019.


"With Oil under Attack, Trump's Deference to Saudis Returns to the Fore." New York Times, September 17, 2019.


This section was prepared by Paul K. Kerr. Specialist in Nonproliferation. For additional details, see CRS Report RL34544, Iran's Nuclear Program: Status, by Paul K. Kerr.


"Letter of Foreign Minister to UN Secretary General," May 10, 2018.


"Iran Can Resume 20 Per Cent Uranium Enrichment Only in 5 Days: Salehi," Iranian Students News Agency (ISNA), August 22, 2017; "AEOI Chief: Iran Able to Resume 20% Enrichment in Maximum 5 Days," FARS News Agency, August 22, 2017.


Unless otherwise noted, this paragraph is based on "AEOI Chief: Iran No More Remaining Restricted To 300 Kg Ceiling For Enriched Uranium," Fars News Agency, May 8, 2019; "Iran: Report Publishes Text of Supreme National Security Council Statement on Nuclear Deal," Tehran Fararu Online, May 8, 2019; Revision: Iran: President Ruhani Heralds New Nuclear Deal Strategy, Announces 60-Day Deadline, May 8, 2019; Statement from Supreme National Security Council of the Islamic Republic of Iran, May 8, 2019; "Spokesman: Iran to Cross 300kg Uranium Stockpile Borderline in 10 Days," FARS News Agency, June 17, 2019.


"Parliament Speaker's Top Advisor: Iran Not to Extend 60-Day N. Deal Deadline," FARS News Agency, June 16, 2019.


Verification and Monitoring in the Islamic Republic of Iran in Light of United Nations Security Council Resolution 2231 (2015), Report by the Director General, GOV/INF/2019/8. July 1, 2019; Verification and Monitoring in the Islamic Republic of Iran in Light of United Nations Security Council Resolution 2231 (2015), Report by the Director General, GOV/INF/2019/9, July 8, 2019.


Verification and Monitoring in the Islamic Republic of Iran in Light of United Nations Security Council Resolution 2231 (2015), Report by the Acting Director General, GOV/2019/32. August 30, 2019.


"FM Zarif: Tehran Firm to Keep Scaling Down N. Commitments," FARS News Agency, August 27, 2019.


"Iran Official Outlines Conditions for Preservation of the Nuclear Deal," Vision of the Islamic Republic of Iran Network 1, August 28, 2019.


"President After the Meeting of Three Branches' Heads: Iran's Third Step to Begin Friday; Atomic Energy Org. Authorized to Do Whatever Needed in Nuclear Technology, Research/ Iran's Activities within IAEA Framework/ Europe Has Another 60 Days," September 5, 2019. Available at http://president.ir/en/111155.


Verification and Monitoring in the Islamic Republic of Iran in Light of United Nations Security Council Resolution 2231 (2015), Report by the Acting Director General, GOV/INF/2019/10, September 8, 2019.




For additional details, see CRS Report R40094, Iran's Nuclear Program: Tehran's Compliance with International Obligations, by Paul K. Kerr.


"Pompeo crashes Brussels meeting of E.U. diplomats but changes few minds on Iran," Washington Post, May 13, 2019.


For additional detail on U.S. sanctions, see: CRS Report RS20871, Iran Sanctions, by Kenneth Katzman.


The text of the Order can be found at https://www.whitehouse.gov/presidential-actions/executive-order-imposing-sanctions-respect-iron-steel-aluminum-copper-sectors-iran/.


Paul Sonne and Missy Ryan, "Amid tensions with Iran, White House mulls U.S. military request to send more forces to the Middle East," Washington Post, May 23, 2019.


Gordon Lubold and Michael Gordon, "U.S. Deploys Forces to Mideast to Mideast to Deter Iran," Wall Street Journal, May 5, 2019.


Department of Defense Briefing on Iran, May 24, 2019, op. cit.


Doha Madani, "U.S. Sending 1,000 troops to Middle East amid heightened tension with Iran," NBC, June 18, 2019.


Robert Burns, "Officials: US putting troops back in Saudi Arabia," Associated Press, July 21, 2019.


Trump to Send Troops to Saudi Arabia and Emirates. New York Times, September 21, 2019.


Edward Wong, "Trump Imposes New Sanctions on Iran, Adding to Tensions," New York Times, June 24, 2019.


Bradley Peniston, "Operation Earnest Will," at http://www.navybook.com/no-higher-honor/timeline/operation-earnest-will/.


UK Statement on Maritime Security Mission. August 5, 2019.


Australia Joins U.S.-Led Maritime Force Protecting Persian Gulf Shipping. NPR, August 22, 2019.


See "Israel to join US-led coalition in Persian Gulf." Anadolu Agency, August 7, 2019.


For analysis on Syria and on Lebanon see CRS Report RL33487, Armed Conflict in Syria: Overview and U.S. Response, coordinated by Carla E. Humud and CRS Report R44759, Lebanon, by Carla E. Humud.


"Iran's Playbook—Deconstructing Tehran's Regional Strategy," Soufan Center, May 2019, at https://thesoufancenter.org/irans-playbook-deconstructing-tehrans-regional-strategy-by-the-soufan-center/.


Ambassador Brian Hook, "The Iranian Regime's Transfer of Arms to Proxy Groups," November 29, 2018.


Department of State. Country Reports on Terrorism: 2017.


"As Israel's anti-Iran strategy shifts into higher gear, worries of fresh conflict grow."Al Monitor, September 13, 2019.


Alyza Sebenius, "Trump Says 'Always a Chance' of War with Iran But Prefers Talks," Bloomberg, June 5, 2019.


"Iran's Foreign Minister Proposes Modest Deal to End Impasse with U.S," New York Times, July 18, 2019.


Department of State, Secretary Pompeo's Call with Omani Sultan Qaboos bin Sa'id Al Sa'id. May 16, 2019.


"Trump: Sen. Rand Paul to help with Iran negotiations," Politico, July 19, 2019.


"Iran, U.A.E. Discuss Maritime Security Amid Heightened Tensions in Gulf." Wall Street Journal, July 30, 2019.


"Bolton's departure allegedly pegged to disagreement over lifting sanctions on Iran." Washington Post, September 14, 2019.


"France reportedly offers Iran $15bn Instex credit line for sanctions-protected trade." Intellinews, August 7, 2019.


The White House, A Look at the U.S. Strategy for Iran, February 13, 2019, at https://www.whitehouse.gov/articles/look-u-s-strategy-iran/.


Kathleen J. McInnis (2005) Extended deterrence: The U.S. credibility gap in the Middle East, The Washington Quarterly, 28:3, 169-186, DOI: 10.1162/0163660054026489.


"Trump Administration Prepares Multiple Military Options for Iran, Including Airstrikes and Setting Up Ground Invasion." Newsweek, May 14, 2019.


Emanuele Ottolenghi, "Only Crippling Sanctions Will Stop Iran," New York Times, March 2, 2012.


Eric Schmitt and Julian Barnes, "White House Reviews Military Plans against Iran, in Echoes of Iraq War," New York Times, May 13, 2019.


Adam Taylor, "A conflict with Iran would not be like the Iraq War. It would be worse," Washington Post, May 14, 2019.


IISS, The Military Balance: 2019, Iran.


Grace Segers, "Bernie Sanders says Trump 'helped create the crisis' in Iran," CBS News, June 22, 2019.


Some analysts have suggested that the 1973 War Powers Resolution (P.L. 93-148), which requires the President to notify Congress when U.S. armed forces are introduced into hostilities or situations of imminent hostilities and withdraw those forces within 60 to 90 days unless Congress authorizes such action, might also represent a check on the President's authority under Article II of the Constitution. Scott Anderson, "When Does the President Think He Can Go To War With Iran?" Lawfare, June 24, 2019. For more, see CRS Report R42699, The War Powers Resolution: Concepts and Practice, by Matthew C. Weed.


Nicholas Wu, "Trump says he doesn't want war, but Sen. Cotton called for 'retaliatory strikes' on Iran," USA Today, June 16, 2019.


Lindsey Graham, Twitter, June 15, 2019. https://twitter.com/LindseyGrahamSC/status/1140063250438078466.


For more on arguments around congressional attempts to limit military action via appropriations, see CRS Report R41989, Congressional Authority to Limit Military Operations, by Jennifer K. Elsea, Michael John Garcia, and Thomas J. Nicola.


Saagar Enjeti and Jordan Fabian, "EXCLUSIVE: Trump: I do not need congressional approval to strike Iran," The Hill, June 24, 2019.


President Trump (@realDonaldTrump), Twitter, June 25, 2019, 7:42 AM.


Ned Price, "Why Mike Pompeo Released More bin Laden Files," Atlantic, November 8, 2017. See also Barbara Slavin, "Expediency and betrayal: Iran's relationship with al-Qaeda," Al-Monitor Iran Pulse, September 7, 2018.


For background, see CRS Report R43983, 2001 Authorization for Use of Military Force: Issues Concerning Its Continued Application, by Matthew C. Weed.


Engel & Deutch Receive State Department Answer on Old War Authorizations & Iran, Committee on Foreign Affairs Press Release, June 28, 2019. While the Trump Administration has previously stated that it views the 2001 AUMF as authorizing U.S. action in defense of partner forces participating in counter-Islamic State operations in Syria, one analyst argues that the State Department's letter represents "the first time the executive branch has publicly extended this collective self-defense theory to the 2002 AUMF." Scott R. Anderson, "Parsing the State Department's Letter on the Use of Force Against Iran," Lawfare, July 3, 2019.


Tess Bridgeman and Ryan Goodman, "Unpacking the State Dept Acknowledgment that 2001 and 2002 AUMFs Don't Authorize War Against Iran," Just Security, July 3, 2019.


The quotes in this table are from various public sources available to congressional clients from the authors upon request.