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

Updated January 6, 2020 (R45795)
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Since May 2019, U.S.-Iran tensions have heightened significantly, and evolved into conflict after U.S. military forces killed Qasem Soleimani, the commander of the Iran's Islamic Revolutionary Guard Corps-Quds Force (IRGC-QF) and one of Iran's most important military commanders, in a U.S. airstrike in Baghdad on January 2, 2020.

In 2018, the Trump Administration withdrew from the 2015 multilateral nuclear agreement with Iran (Joint Comprehensive Plan of Action, JCPOA), and since mid-2019 has taken several steps in its campaign of applying "maximum pressure" on Iran. Apparently in response to the maximum pressure campaign, 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, attacked facilities used by U.S. military personnel in Iraq, and downed a U.S. unmanned aerial vehicle. As part of an effort its leaders term "maximum resistance," Iran has also reduced its compliance with the provisions of the JCPOA. The Administration has been deploying additional military assets to the region to try to deter future Iranian actions.

The U.S.-Iran tensions have the potential to escalate into all-out conflict in the wake of Soleimani's killing. Iran's materiel support for armed factions throughout the region, including its provision of short-range ballistic missiles to these factions, and Iran's 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. The United States military has the capability to undertake a range of options against Iran, both against Iran directly and against its regional allies and proxies. 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 future such Iranian attacks.

President Donald Trump has consistently stated that he wants 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 have sought to mediate to try to de-escalate U.S.-Iran tensions by encouraging 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. The strike on Soleimani, who is revered among many factions in Iran for his success in orchestrating Iran's strategy of exerting regional influence, has produced an emotional response among Iran's leaders and population. Iran's Supreme Leader and IRGC leaders have stated that Iran will retaliate militarily, although at an unspecified time and in unstated ways, seemingly dimming the prospects for U.S.-Iran talks on a new JCPOA at least in the near term.

Members of Congress have received additional information from the Administration about the causes of the U.S.-Iran tensions and Administration 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 since the 1979 Islamic Revolution in Iran. U.S. officials and official reports consistently identify Iran's support for militant armed factions in the Middle East region 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 thwart Iran's purchase of new conventional weaponry and development of 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 Senior Administration officials explain Administration policy as the application of "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 officials deny that the policy is intended to stoke economic unrest in Iran.3

As the Administration has pursued its policy of maximum pressure, including imposing sanctions beyond those in force before JCPOA went into effect in January 2016, bilateral tensions have escalated significantly. Key developments that initially heightened tensions include the following.

Iran's Initial Responses to the U.S. Pressure Steps

Iran responded to the U.S. maximum pressure campaign in part by demonstrating its ability to harm global commerce and other U.S. interests and to raise concerns about Iran's nuclear activities. Iran might have sought to cause international actors, including those 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 (see Figure 1 for a map of Iran-supported groups). 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

Figure 1. Selected Iran-supported Groups

Source: "Iran Military Power: Ensuring Regime Survival and Securing Regional Dominance," Defense Intelligence Agency (DIA), November 2019.

Some of the most significant actions by Iran-linked forces are the following:

Iran and U.S. Downing 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 (see Figure 3). 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.23 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 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. 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. 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."24 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."25 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.

On August 15, following a reported pledge by Iran not to deliver the oil cargo to Syria, a Gibraltar court ordered the ship (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.26 The ship apparently delivered its oil to Syria despite the pledge27 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 released the Stena Impero.

Separate from the UK-Iran dispute over the Grace I and the Stena Impero, Iran seized an Iraqi tanker on August 5, 2019, for allegedly smuggling Iranian diesel fuel to "Persian Gulf Arab states."28

Parallels to Past Incidents in the Gulf29

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 "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 in September 201930

On September 14, 2019, 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."31 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."32 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 nearly 20 targets at those Saudi sites.33 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. President Trump stated on September 16 that he would "like to avoid" conflict with Iran and the Administration did not retaliate militarily. U.S. officials did announce modest increases in U.S. forces in the region and some new U.S. sanctions on Iran. Secretary of State Pompeo visited Saudi Arabia and the UAE during September 18-19 to discuss responses to the attack, and in his press conferences in the region he stated an intent to use diplomacy to try to resolve the crisis.

The attacks on the Saudi infrastructure raised several broad questions, including

U.S. Sanctions Responses to Iranian Provocations

As tensions have increased with Iran, the Trump Administration has undertaken a number of steps to try to further increase economic pressure on Iran, to weaken it strategically, and compel Iran to negotiate a broader resolution of U.S.-Iran differences.

JCPOA-Related Iranian Responses35

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.

Tehran also threatened to reconstitute and resume the country's pre-JCPOA nuclear activities.

Several meetings of the JCPOA-established Joint Commission since the U.S. withdrawal have not produced a firm Iranian commitment to the agreement. 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, 2019, 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.

Beginning in July 2019, the International Atomic Energy Agency (IAEA) verified that some of Iran's nuclear activities were exceeding JCPOA-mandated limits; the Iranian government has since increased the number of such activities. Specifically, according to IAEA reports, Iran has exceeded JCPOA-mandated limits on its heavy water stockpile, the number of installed centrifuges in Iran's pilot enrichment facility, Iran's LEU stockpile, and the LEU's concentration of the relevant fissile isotope uranium-235. In addition, Tehran is conducting JCPOA-prohibited research and development activities, as well as centrifuge manufacturing, and has also begun to enrich uranium at its Fordow enrichment facility.

Iranian President Hassan Rouhani, in a November 5 speech, explained that Tehran still supports negotiations with the P4+1:

In the next two months, we still have a chance for negotiations. We will negotiate and talk with each other, and if we find the right solution, and the solution is in lifting of the sanctions, and that we will be able to sell our oil easily, we will be able to use our money in banks easily, and other issues that they have imposed sanctions on, such as metals and insurance, and if they lift sanctions fully, we will also return to the previous conditions fully.

The Iranian government announced on January 5 what an official news agency report described as "the fifth and final step in reducing" Tehran's JCPOA commitments. The statement explains that Iran "will set aside the final operational restrictions under the JCPOA which is 'the restriction on the number of centrifuges.' " The January 5 announcement provides no details regarding concrete changes to Iran's nuclear program, but the term "restrictions" may refer to the JCPOA-mandated limits on installed centrifuges at the country's commercial enrichment facility. Iran has adhered to these restrictions. Tehran has stated that the government will continue to cooperate with the IAEA and abide by the JCPOA's monitoring and inspections provisions. The January 5 announcement adds that "[i]n case of the removal of sanctions and Iran benefiting from the JCPOA," Iran "is ready to resume its commitments" pursuant to the agreement.

Tensions Escalate into Conflict: Iraq is the Arena (December 2019-January 2020)

In early December 2019, press reports and U.S. officials detailed signs that Iran might be focusing on exerting pressure on U.S. interests in Iraq. Iran reportedly supplied short range missiles to allied forces inside Iraq,36 and a series of indirect fire attacks in mid-December 2019 targeted Iraqi military facilities where U.S. forces are co-located.37In response, Secretary Pompeo issued a statement saying, "We must also use this as an opportunity to remind Iran's leaders that any attacks by them, or their proxies of any kind, that harm Americans, our allies, or our interests will be answered with a decisive U.S. response."38 Secretary of Defense Mark Esper stated that he urged Iraqi Prime Minister Adel Abd Al Mahdi to "take proactive actions…to get that under control."39

On December 27, a rocket attack on a base near Kirkuk in northern Iraq killed a U.S. contractor and wounded four U.S. service members and two Iraqi service members. Two days later, the U.S. launched retaliatory airstrikes on five facilities (three in Iraq, two in Syria) used by the Iran-backed Iraqi armed group Kata'ib Hezbollah, a U.S.-designated Foreign Terrorist Organization to which the U.S. attributed the December 27 and other attacks. A Pentagon statement said the strikes "will degrade KH's ability to conduct future attacks."40 KH leader and leading figure in the Iraqi-state affiliated Popular Mobilization Forces Abu Mahdi al Muhandis said dozens of fighters were killed and injured and promised a "very tough response" on U.S. forces in Iraq.41

Iraqi leaders, including Prime Minister Abd Al Mahdi, who in recent years has sought to maintain good relations with both the United States and Iran, criticized the strikes as a "violation of Iraqi sovereignty."42 Abd Al Mahdi resigned in December 2019, but continues to serve in a caretaker role while Iraqi political leaders negotiate transition arrangements. U.S. forces remain in Iraq at the invitation of the Iraqi government, but Iran-aligned Iraqis have called for the expulsion of U.S. forces. Escalation in Iraq between the U.S. and Iran and its proxies poses a serious challenge for the Iraqi government and for U.S.-Iraq relations.

The attacks came as Iran has sought to preserve its political influence amidst large-scale demonstrations in which hundreds of protestors have been killed by security forces.43 The U.S. government designated Iran-linked Iraqi groups and individuals in 2019 for involvement in human rights abuses and attacks on Iraqi protesters. In a December 6, 2019 press briefing announcing those designations, Assistant Secretary of State for Near Eastern Affairs David Schenker said,

the United States Government will work with anyone in the Iraqi Government who is willing to put Iraqi interests first.... This is a sine qua non. But we see in the process of establishing a new government or determining who the next prime minister will be that Qasem Soleimani is in Baghdad working this issue. It seems to us that foreign terrorist leaders, or military leaders, should not be meeting with Iraqi political leaders to determine the next premier of Iraq, and this is exactly what the Secretary says about being perhaps the textbook example of why Iran does not behave and is not a normal state. This is not normal. This is not reasonable. This is unorthodox and it is incredibly problematic, and it is a huge violation of Iraqi sovereignty.44

On December 31, 2019, two days after the U.S. airstrikes against KH targets in Iraq and Syria, supporters of Kata'ib Hezbollah and other Iran-backed Iraqi militias surrounded the U.S. Embassy in Baghdad, forcing their way into the compound and setting some outer buildings on fire. Demonstrators (who differed in both profile and motivation from those protesting elsewhere in Baghdad since October) withdrew after their leaders said they obtained acting Prime Minister Abdul Mahdi's promise for "serious work" on a parliamentary vote to expel U.S. forces from the country, a long-sought goal of Iranian-backed militias in Iraq.45

No U.S. personnel were harmed at the Embassy, but Secretary Esper announced the deployment of an additional infantry battalion "in response to increased threat levels against U.S. personnel and facilities, such as we witnessed in Baghdad."46 President Trump tweeted that Iran, which "orchestrat[ed the] attack," would "be held fully responsible for lives lost, or damage incurred, at any of our facilities. They will pay a very BIG PRICE!"47

Iranian President Hassan Rouhani, in a November 5 speech, explained that Tehran still supports negotiations with the P4+1:

In the next two months, we still have a chance for negotiations. We will negotiate and talk with each other, and if we find the right solution, and the solution is in lifting of the sanctions, and that we will be able to sell our oil easily, we will be able to use our money in banks easily, and other issues that they have imposed sanctions on, such as metals and insurance, and if they lift sanctions fully, we will also return to the previous conditions fully.48

U.S. Escalation: Drone Strike Kills Qasem Soleimani

On January 2, 2020, the Department of Defense announced in a statement that the U.S. military had killed IRGC-QF Commander Major General Qasem Soleimani in a "defensive action." The statement cited Soleimani's responsibility for "the deaths of hundreds of Americans and coalition service members" and his approval of the Embassy blockade, and stated that he was "actively developing plans to attack American diplomats and service members in Iraq and throughout the region." According to subsequent media reports, Soleimani was killed in a U.S. drone strike while leaving Baghdad International Airport early on the morning of January 3 local time; KH/PMF leader Al Muhandis and other Iranian and Iraqi figures also were killed in the strike. Iranian Supreme Leader Khamene'i declared three days of national mourning and vowed revenge for Soleimani's killing. Iraqi Prime Minister Abd al Mahdi requested that the Iraqi parliament hold "an emergency session to take the appropriate legislative measures in a manner that preserves the dignity, security and sovereignty of Iraq." Iraq's Council of Representatives (CoR) on January 5, 2020, voted to direct the government "to work towards ending the presence of all foreign troops on Iraqi soil," according to the media office of the Iraqi Parliament. However, whether and how the vote will translate into an alteration of the U.S. military presence in Iraq remains uncertain. For information on U.S.-relations with Iraq, see CRS In Focus IF10404, Iraq and U.S. Policy, by Christopher M. Blanchard.

Soleimani was widely regarded as one of the most powerful and influential figures in Iran, perhaps second only to Khamene'i, to whom Soleimani had a direct channel (see textbox below).49 Some analysts argue that his death is likely to have a dramatic impact on Iran's capabilities, with one expert describing him as "the military center of gravity of Iran's regional hegemonic efforts" and "an operational and organization genius who likely has no peer in the upper ranks of the Islamic Revolutionary Guard Corps."50 Others contend that while Soleimani was undoubtedly important, "he was only the agent of a government policy that preceded him and will continue without him."51

IRGC-QF Commander Qasem Soleimani and Successor

Qasem Soleimani was born in March 1957 in Kerman Province (southeast Iran). He joined the IRGC at its inception in 1979, serving in his home province. He participated in post-revolution suppression of Kurdish insurgents in northwestern Iran. He commanded an IRGC unit and then its 41st Sarollah Division during the Iran-Iraq war. The division was deployed back to Soleimani's home province of Kerman after that war and was tasked with combating drug smugglers. He was still in that position when he was appointed as commander of the IRGC-QF in 1998. His main priority after taking command of the IRGC-QF was to work with Afghans of Tajik origin ("Northern Alliance") against the Taliban regime, which at the time was a strategic adversary of Iran.

After 2001, when the Taliban was ousted by the U.S.-led military engagement in Afghanistan in the aftermath of the September 11, 2001, attacks on the United States, the IRGC-QF turned its attention to the broader Middle East region. Soleimani's success in expanding Iran's regional influence through the IRGC-QF's formation of pro-Iranian militias in several countries has made him a national hero in Iran. The regime afforded him wide publicity inside Iran as an able strategist who combatted Iran's adversaries from the front lines of regional conflicts.

In early January, Supreme Leader announced that he was appointing deputy IRGC-QF commander, IRGC Brigadier General Ismail Qaani as the head of the Qods Force. He and other IRGC figures stated that Qods Force operations would proceed as they were under Soleimani. On the other hand, Qaani has been widely considered less charismatic than Soleimani and perhaps less familiar with Iraqi, Syrian, and Lebanese allies of Iran than was Soleimani. Qaani is about 62 years old. As was Soleimani, Qaani has been sanctioned by the United States under various Executive Orders.

Potential Iranian Responses and Scenarios

Secretary of State Pompeo underscored that the United States is not seeking further escalation, but Iran's leaders, including Supreme Leader Ali Khamene'i, have threatened to retaliate for the Soleimani killing. Key questions about potential Iranian retaliation include

In several Twitter messages and other statements, President Trump has threatened to respond with significant use of U.S. force if Iran retaliates for the Soleimani killing.

International Responses to the Escalating Tensions and Efforts to De-Escalate

U.S. partner countries and U.N. officials have consistently called for the de-escalation of tensions and the avoidance of war, emphasizing de-escalation in the wake of the Soleimani killing. The EU countries have refused to join the U.S. maximum pressure campaign as a consequence of Iran's provocative acts, although the UK, France, and Germany have urged Iran to negotiate a new JCPOA that includes limits on Iran's missile development.55 Some U.S. allies have joined a U.S. effort to deter Iran from further attacks on shipping in the Gulf. At the same time, even after the Soleimani killing and threats of Iranian retaliation, as well as Iran's additional scaling back of compliance with the JCPOA, EU officials said they still hoped the JCPOA could be preserved.56

The United States and Iran do not have diplomatic relations and there have been no known high-level talks between Iran and Administration officials since the Trump Administration withdrew from the JCPOA. Prior to the Soleimani killing, various third country leaders, such as Japanese Prime Minister Shinzo Abe in mid 2019 and again in a visit to Iran in December 2019, have sought to move Tehran and Washington toward direct talks. President Trump 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.57

Several Gulf countries 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.58 Whereas Qatar has consistently maintained relations with Iran, a UAE delegation that visited Tehran in late July undertook the first UAE security talks with Iran since 2013.

In August 2019, French President Macron produced some movement toward U.S.-Iran 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 but, at a press conference at the close of the summit, President Trump reiterated his willingness, in principle, to meet with Iranian President Hassan Rouhani, presumably during the U.N. General Assembly meetings in New York in September. Some press reports indicated that President Trump considered supporting a French credit line proposal discussed below by approving sanctions waivers and exceptions to facilitate the credit line, possibly as an incentive for Iran to meet with him.59 However, in the wake of the September 14, 2019 attacks in Saudi Arabia and since, the Supreme Leader has 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. The Soleimani killing seems to have moved any U.S.-Iran talks further from realization.

Iran-Focused U.S. Military Deployments since Mid-2019

To try to deter further Iranian attacks, 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 additional deployments as of October 2019 had added 14,000 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.60 Defense Department officials indicated that the additional deployments have mostly restored forces who were redeployed from the region a few years ago, and do not represent preparation for any U.S. offensive against Iran.61

A key question is whether the increase in U.S. force levels in the region—coupled with President Trump's threats of further action if Iran retaliates for the Soleimani killing—will deter Iran from retaliating or from further provocations. In November 2019, before the Soleimani killing seemingly provided increased Iranian inclination to attack U.S. targets, the commander of U.S. Central Command, General Kenneth McKenzie, stated that the U.S. deployments during May—October might have deterred Iran from attacking U.S. targets, but that "I wouldn't rule [another Iranian attack like the September 14 attack on Saudi oil infrastructure] out going forward."68 Referring to recent rioting in Iran in response to a reduction in fuel subsidies, General McKenzie added that "Iran is under extreme pressure" and is trying to "crack the [maximum pressure] campaign" with attacks to provoke an American military response.

Gulf Maritime Security Operation

In addition to deploying more U.S. forces, 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, the Bab el-Mandeb Strait, and the Suez Canal. Defense Secretary Mark Esper told reporters on August 28, 2019, "I am pleased to report that Operation Sentinel is up and running," but the coalition, termed the International Maritime Security Construct (IMSC), was formally inaugurated in Bahrain in November 2019. It consists of seven nations (United States, UK, UAE, Saudi Arabia, Bahrain, Albania, and Australia) operating four sentry ships at crucial points in the Gulf.69 Qatar and Kuwait have pledged to join the mission in the near future, and Canada and "some European countries" are described as having "expressed interest in the effort."70 The IMSC appears to supplement longstanding multilateral Gulf naval operations that have targeted smuggling, piracy, the movement of terrorists and weaponry, and other potential threats in the Gulf.

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.71 Defense Department officials have not listed Israel as a participant in IMSC to date. 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.

France reportedly intends to lead a separate maritime security mission (headquartered in Abu Dhabi) in the Gulf starting in early 2020; the Netherlands and several other European countries have expressed interest. India has sent some naval vessels to the Gulf to protect Indian commercial ships. And, in December 2019, Japan sent vessels to protect Japanese shipping, also separate from the IMSC.

U.S. Military Action: Options and Considerations

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."72 As such, the military could be used in a variety of ways to try to 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 further 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 set back the political prospects of Iranians sympathetic to a change of regime. As an example, Soleimani was mourned publicly by millions of Iranians and his killing seems to have unified the Iranian population behind the regime, at least temporarily. 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.

Secretary of Defense Mark Esper and other U.S. officials have stated that the additional U.S. deployments since May are intended to deter Iran from taking any further provocative actions and position the United States to defend U.S. forces and interests in the region.73 Iranian attacks after previous U.S. deployments could be viewed to suggest that deploying additional assets and capabilities might not necessarily succeed in deterring Iran from using military force.

On the other hand, there are risks to military inaction that might potentially outweigh 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 IMSC discussed above. Not all of these options are mutually exclusive, nor do they represent a complete list of possible options, implications, and risks. And, the Congress has assessed its role in any decisions regarding whether to undertake military action against Iran, as 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:

At the same time, there is potential for some U.S. costs to be offset by contributions. The Persian Gulf states and other countries have a track record of offsetting U.S. costs for Gulf security. In the current context, President Trump stated in October 2019 that Saudi Arabia would pay for the deployment of additional U.S. troops and capabilities to assist with the territorial defense of Saudi Arabia and the deterrence of Iranian aggression in the region overall, and subsequent reports indicate that U.S. and Saudi officials are negotiating a cost-sharing arrangement for the new deployments.80

Congressional Responses

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

In June 2019, amidst attacks against tankers in the Gulf of Oman and Iran's shootdown of a U.S. military drone, some Members expressed concern about the legal justification for military operations in or against Iran. On June 22, Senator Bernie Sanders 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."81 Other Members positioned themselves as more generally supportive of broad discretion for the Administration to act. Senator Tom Cotton 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 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

President Trump said in a June 24 interview that he believes he has the authority to direct strikes against Iran, and said, "I do like keeping them [Congress] abreast, but I don't have to do it, legally."84 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."85

The prospect of U.S. military action against Iran in the wake of the September attacks on Saudi oil facilities at Abqaiq and Khurais prompted additional responses from several Members of Congress. President Trump's statement that the United States was "locked and loaded" but "waiting to hear from the Kingdom as to who they believe was the cause of this attack, and under what terms we would proceed" drew particular congressional attention, with several Members emphasizing, as Representative Cicilline wrote, that "If the President wants to use military force, he needs Congress—not the Saudi royal family—to authorize it."86 Other Members, while generally backing the Administration's assessment that Iran was behind the attacks, argued that time should be given to verify intelligence conclusions.87 Senator Graham described the attack on Abqaiq and Khurais as "literally an act of war" that Iran committed because it interpreted the President's decision to call off airstrikes in response to the June drone shootdown as a "sign of weakness"; President Trump rejected that characterization, describing his approach as "a sign of strength that some people just don't understand!"88

The buildup of U.S. forces in the region in response to Iranian activities has also attracted congressional attention. At a December 5, 2019, hearing with Under Secretary of Defense for Policy John Rood, Senator Josh Hawley said the Pentagon had "made multiple contradictory public statements" with regard to reports of additional U.S. force deployments. Senator Hawley also pressed Under Secretary Rood on "what it is exactly that we're aiming to deter," arguing that "regional stability and the absence of an attack on American forces are…very different" and that "if our aim is to prevent all conflict in the region, we're going to be sending a lot more than 14 or 28 or 100,000 ground troops."89 Section 1227 of the FY2020 National Defense Authorization Act (NDAA, P.L. 116-48) requires an Administration report to Congress on diplomatic and military channels of deconfliction with Iran to "prevent miscalculation" that could "lead to unintended consequences, including unnecessary or harmful military activity."

The killing of IRGC-QF Commander Soleimani in a U.S. drone strike in Baghdad in January 2020 also prompted some Members to raise questions about the authority under which it was conducted. House Speaker Nancy Pelosi said in a statement that the Administration launched the strike that killed Soleimani "without an Authorization for Use of Military Force (AUMF) against Iran" and "without the consultation of the Congress," and called for Congress to be "immediately briefed on this serious situation."90

Legislation and AUMF Considerations

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.91 For instance, Section 1284 of the FY2020 NDAA states that "Nothing in this Act, or any amendment made by this Act, may be construed to authorize the use of military force, including the use of military force against Iran or any other country." Similarly, Section 9024 of Division A of H.R. 1158, the Consolidated Appropriations Act, 2020, states that "Nothing in this Act may be construed as authorizing the use of force against Iran." However, House-passed measures to 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), such as Section 1229 of H.R. 2500, were not included in conference text.

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."92

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."93 As passed by the House, Section 9025 of H.R. 2740 would repeal the 2001 AUMF within 240 days of enactment.94

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."95 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.96

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 costs, financial and otherwise. With that in mind, Congress could consider the following:

Figure 2. Iran, the Persian Gulf, and the Region

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

Figure 3. 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.


British-Flagged Tanker Leaves Iran, Two Months After It Was Seized. New York Times, September 27, 2019.


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


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


"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.


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/.


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.


"Iran is Secretly Moving Missiles into Iraq, U.S. Officials Say," New York Times, December 4, 2019; "U.S. Warship in the Gulf Seizes Alleged Iranian Missile Parts," Al Jazeera, December 5, 2019.


There are approximately 5,000 U.S. forces in Iraq at the invitation of the Iraqi government as part of Operation Inherent Resolve, launched in 2014 to defeat the Islamic State.


Press Statement On Attacks by Iran's Proxies in Iraq, Secretary of State Michael R. Pompeo, December 13, 2019.


Secretary Esper Holds an In-Flight Media Availability, U.S. Department of Defense, December 16, 2019.


U.S. Department of Defense, Statement From Assistant to the Secretary of Defense Jonathan Hoffman, December 29, 2019.


"Top Iraq militia chief warns of tough response to U.S. air strikes," Reuters, December 30, 2019.


"Iran slams 'terrorist' raids by US on Shia militias in Iraq, Syria," Al Jazeera, December 30, 2019.


See CRS Insight IN11195, Iraq: Protests, Transition, and the Future of U.S. Partnership, by Christopher M. Blanchard.


Assistant Secretary for Near Eastern Affairs David Schenker on Iraqi Global Magnitsky Designations, U.S. Department of State, December 6, 2019.


Ghassan Adnan and Isabel Coles, "Militia Supporters Retreat From U.S. Embassy Site in Iraq," Wall Street Journal, January 1, 2019.


Department of Defense, SD Statement on Deployment of 82nd Airborne Division, December 31, 2019.


President Trump (@realDonaldTrump), Twitter, December 31, 2019, 7:44 AM.


"Iran President Announces Fourth Step in Scaling Back Nuclear Commitments–Text," November 7, 2019 (Text of speech by Iranian President Hassan Rouhani at opening ceremony for Azadi Innovation Factory in Tehran published by website of the Presidency of the Islamic Republic of Iran, November 5, 2019).


Dexter Filkins, "The Shadow Commander," New Yorker, September 23, 2013.


Frederic Hof, quoted in David Wemer, "Soleimani killing threatens to break open US-Iranian conflict," Atlantic Council, January 3, 2020.


George Packer, "Killing Soleimani Was Worse Than a Crime," The Atlantic, January 3, 2020.


Senate Select Committee on Intelligence. Worldwide Threat Assessment of the U.S. Intelligence Community. January 29, 2019.


The report can be accessed at https://www.dia.mil/Portals/27/Documents/News/Military%20Power%20Publications/Iran_Military_Power_LR.pdf


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


European powers back U.S. in blaming Iran for Saudi oil attack, urge broader talks. Reuters, September 23, 2019.


EU regrets Iran nuclear moves but hopes to keep deal alive. Associated Press, January 6, 2020.


"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.


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; DOD Statement on Deployment of Additional U.S. Forces and Equipment to the Kingdom of Saudi Arabia. October 11, 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.


DOD Statement on Deployment of U.S. Forces and Equipment to the Kingdom of Saudi Arabia. September 26, 2019.


DOD Statement on Deployment of Additional U.S. Forces and Equipment to the Kingdom of Saudi Arabia. October 11, 2019.


SD Statement on Deployment of 82nd Airborne Division, December 31, 2019.


U.S. Commander Warns of Iranian Attack in Middle East. New York Times, November 23, 2019.


Department of Defense. International Unit Serves Critical Role in Persian Gulf. November 25, 2019.




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


DOD Statement on Deployment of Additional U.S. Forces and Equipment to the Kingdom of Saudi Arabia, October 11, 2019; "U.S. Military has Enough Capability in the Middle East for Now: Esper," Reuters, December 9, 2019.


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.


"Pentagon Advances Talks to Set Terms for Expanding Saudi Defense Mission." Washington Post, November 28, 2019.


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


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.


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.


John Bennett, "Democrats object to Trump's threatening Iran over Saudi oil attack," Roll Call, September 16, 2019.


Joe Gould, "Senate Republicans not ready for US military action against Iran," Defense News, September 17, 2019.


Caroline Kelly, "Trump rebuts Graham: My response to Iran 'was a sign of strength,'" CNN, September 18, 2019.


Senate Armed Services Committee Holds Hearing on National Defense Strategy Implementation, CQ Congressional Transcripts, December 5, 2019.


Pelosi Statement on Airstrike in Iraq Against High-Level Iranian Military Officials, January 2, 2020.


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.


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.


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.