In the early hours of Jan. 3, the Trump administration chose to dramatically escalate its regional stand-off with Iran, specifically by killing Iranian Major General Qassem Soleimani in a targeted drone strike on the road leading to Baghdad International Airport. Killed alongside Soleimani was Abu Mahdi al-Mohandes, deputy commander of Iraq’s quasi-official Hashd al-Shaabi, or Popular Mobilization Forces (PMFs) and leader of the Iraqi militia and PMF Keta’ib Hezbollah, which the United States targeted in a series of Dec. 29 airstrikes for its alleged involvement in rocket attacks on facilities housing U.S. personnel.

The U.S. Defense Department later released a statement indicating that it had taken this “decisive defensive action” at the direction of President Trump in order to “deter[] future Iranian attack plans.” Soleimani, it asserted, was “responsible for the deaths of hundreds of American and coalition service members and the wounding of thousands more,” including a Dec. 27 rocket attack that killed a U.S. contractor outside Kirkuk and the Dec. 31 assault on the U.S. Embassy in Baghdad, Iraq. Notably, the U.S. strike followed closely on the heels of remarks by Secretary of Defense Mark Esper in which he indicated that the United States would “take preemptive action” to protect against Iranian attacks moving forward. Killing Soleimani appears to be the first application of this new policy. The next morning, Secretary of State Mike Pompeo asserted that intelligence reports indicated that Soleimani had been “actively plotting” to “take big action … that would have put hundreds of lives at risk,” and that the United States had acted to eliminate “imminent threats to American lives.”

As the longtime leader of the paramilitary Quds Force within Iran’s Islamic Revolutionary Guard Corps, Soleimani almost undoubtedly has been involved in countless attacks on American forces in Iraq and elsewhere. He also played a central role in cultivating and supporting several of Iraq’s Shiite militias, which have—even before they became PMFs affiliated with the Iraqi government—sought to dominate Iraqi politics, including most recently through the violent suppression of Iraq’s popular protest movement. In this sense, many observers are likely to see Soleimani’s removal as a significant victory.

That said, the targeted killing of such a senior Iranian official—along with one of his Iraqi counterparts—is almost certain to have serious ramifications for various U.S. interests in the region. Iran’s Supreme Leader, Ayatollah Ali Khamenei, has already warned that “a harsh retaliation is waiting,” while Iraqi Prime Minister Adel Abdul-Mahdi has called for an emergency parliamentary session to “take legislative steps and necessary provisions to safeguard Iraq’s dignity, security and sovereignty”—a debate that may well end with the revocation of Iraqi consent for the U.S. military presence in the country. The threat of retribution was seen as serious enough that the State Department has advised that all Americans in Iraq immediately depart by whatever means available.

These policy ramifications are important and underscore how difficult a decision it must have been whether or not to pursue this operation. But this in turn raises another question: On what grounds did Trump claim the legal authority to undertake the Jan. 3 strike that killed Soleimani unilaterally, without informing Congress or seeking the consent of the Iraqi government?

In this piece, I focus on the U.S. domestic law part of the answer to this question. International law is also an important and complex consideration that I intend to address separately in a later piece. Moreover, while there are good arguments that international law should bear on the president’s domestic legal authority, the Trump administration most likely does not see itself as constrained by international law in this way. Thus the two analyses can stand separately from one another.

Throughout, I focus on the legal views of the executive branch. These views are not necessarily legally correct, nor do I necessarily agree with them. Yet the federal courts have resisted reaching the merits of any legal challenges to these views, and Congress has not stepped up to limit or disturb them. Absent such limitations, the views of the executive branch—the institution responsible for interpreting and applying the law under the U.S. constitution—are as close as one can get to what is officially “lawful” under U.S. law. These views are also the ones that will directly inform executive branch decisions to use military force, making them of special importance.

Even by this deferential metric, however, the Soleimani strike raises serious questions. While we don’t know the exact domestic legal argument that the Trump administration is relying on, the decision to kill Soleimani pushes against certain aspects of how the president’s authority to use military force—both constitutional and statutory—have been construed in the past. This does not mean that these arguments were legally unavailable to the Trump administration or that its actions were unlawful. But it does mean that these actions’ legitimacy may be more vulnerable to criticism, which may in turn encourage new efforts to check his authority through the legislative and political processes.

Article II Authority

Executive branch lawyers—primarily those in the Justice Department’s Office of Legal Counsel (OLC), the main office responsible for formulating the U.S. government’s internal legal views—generally maintain that, at least absent any legislation to the contrary, Article II of the Constitution gives the president the legal authority to use military force overseas so long as (a) he does so pursuant to important U.S. interests and (b) the operation in question is limited enough in nature, scope and duration that it falls below the threshold of what requires congressional authorization under the Constitution. Both prongs of this test are derived from—and thus tend to be informed by—historical U.S. practice. Neither is particularly restrictive.

In its current form, the first “national interests” prong essentially requires only that there be some reasonable nexus between the military operation in question and a U.S. foreign policy interest. While there is debate as to what extent the president’s decision to pursue the Jan. 3 strike actually serve the national interests, the Justice Department views this prong as “a question of policy more than law” on which it largely defers to the president and his policy advisers. In this case, the prong seems readily satisfied by Soleimani’s central role in organizing countless violent attacks against U.S. personnel over the past two decades both in Iraq and elsewhere, including the Dec. 27 rocket attack and Dec. 31 assault on the U.S. Embassy in Baghdad.

The second prong, concerning the “nature, scope and duration” of the operation, weighs a number of different considerations and variables. As described by the Justice Department, it generally serves to rule out only “prolonged and substantial military engagements [that] expos[e] ... U.S. military personnel to significant risks over a substantial period[.]” As a one-time strike executed by an unmanned drone without civilian casualties or other substantial collateral damage, the Jan. 3 strike seems to fall short of this threshold on its face. Indeed, it’s arguably more constrained in scope than many other operations that prior presidents have undertaken pursuant to their Article II authority, which have ranged from the deployment of up to 20,000 U.S. troops to Haiti to a weeks-long sustained aerial campaign against the Gaddafi regime in Libya.

But in the legal opinion it issued in relation to the 2018 airstrikes in Syria, the Trump administration’s own Justice Department suggested this analysis should push deeper. Specifically, it stated, “[I]n evaluating the expected scope of hostilities, we also considered the risk that an initial strike could escalate into a broader conflict” and noted that it was “advised that escalation was unlikely” and briefed on “several measures that had been taken to reduce the risk of escalation[.]” Here, experts are almost universally agreed that the targeted killing of Soleimani will likely lead to escalation by Iran. And because Iran is a substantial military power with proxies who are able to target vulnerable U.S. personnel and other American citizens in various corners of the world, such escalation could result in a conflict of very different nature, scope or duration than if similar military action were pursued against a less capable target.

It’s not clear what steps, if any, the Trump administration may have taken to mitigate this risk of escalation. While this risk may not itself put the Jan. 3 strike outside the scope of the president’s Article II authority, it certainly raises major questions—including about the seriousness with which the Trump administration takes the legal standards it has put forward in its own prior legal opinions.

Alternatively, the Trump administration may not see itself as subject to these limitations, even if it has suggested as much in prior legal opinions and reports to Congress. As Jack Goldsmith has pointed out previously, OLC has thus far declined to revoke at least two opinions from shortly after the Sept. 11 attacks that assert even broader views of the president’s Article II authority in at least certain circumstances. And both Trump and Attorney General William Barr—the two individuals with the authority to supersede OLC opinions—have at times expressed very broad views of the president’s inherent Article II powers, albeit not in this specific context. In other words, it’s possible that the Trump administration—like the early George W. Bush administration—has chosen to depart from certain well-established executive branch legal position to adopt a more idiosyncratic view of the president’s constitutional authority. This could lead it to pursue—or take the risk of triggering—longer and more costly conflicts than other presidents have believed they can pursue without authorization from Congress.

For its part, Congress has taken few steps to limit the president’s Article II authority to use military force. Nor is it entirely clear what limits it could constitutionally impose, given that the scope of the president’s exclusive constitutional authority—which cannot be intruded upon by Congress—has not been settled by the courts. The only substantive limit imposed by the 1973 War Powers Resolution is that the president must secure congressional authorization or else withdraw U.S. forces from any ongoing “hostilities”—a term whose lack of definition has made the law subject to manipulation—within 60-90 days. This may pose an issue if the Jan. 3 strike triggers a more enduring conflict. Alternatively, the Trump administration may share the view of the Nixon administration that this requirement is unconstitutional, even though subsequent administrations moved away from this view.

Regardless, we will know soon if the Trump administration has chosen to rely on its Article II authorities. If it has, then the War Powers Resolution obligates the administration to submit a report to Congress describing the legal basis for the president’s actions within 48 hours—a type of report that the Trump administration has made publicly available in the past. If no such report is forthcoming, then this is most likely a sign that the Trump administration is instead relying on statutory authorization.

Statutory Authority

In the past, the United States has relied on one of two Authorizations for the Use of Military Force (AUMFs) to authorize military operations in Iraq. Both remain on the books and provide the most plausible possible statutory legal basis for the strike that killed Soleimani.

The more famous of the two is the 2001 AUMF, which currently provides the legal authority for U.S. military operations against al-Qaeda and related groups around the world, including those against the Islamic State in Iraq and Syria. The language of this AUMF authorizes “all necessary and appropriate force” against the perpetrators of the Sept. 11 attacks and anyone whom “[the president] determines” has harbored and assisted them—not a category that most see as including the Iranian regime, whose religious views are anathema to those of al-Qaeda. That said, the Trump administration has reportedly suggested in briefings to Congress that the 2001 AUMF could be used to target Iran. The exact reasoning behind this assertion is unclear, but Trump administration officials have reportedly pointed to certain transactional interactions between al-Qaeda and Iran both before and after the Sept. 11 attacks. Such ties are far weaker than what has been used to authorize the use of military force against other groups in the past. But the broad and expressly deferential language of the 2001 AUMF makes its application on the basis of these ties difficult to rule out entirely.

The 2002 AUMF, meanwhile, authorizes the use of force to address “the continuing threat posed by Iraq” without further elaboration. It provided the legal basis for most U.S. military operations in Iraq from 2003 through the U.S. withdrawal in 2011, including prior military operations against Iran-affiliated militias. Since then, it’s primarily served as a redundant authority for the 2001 AUMF for counter-Islamic State operations in Iraq and, in certain circumstances, in Syria. But it could have broader application. As the acting general counsel for the Defense Department described in 2017 remarks, the 2002 AUMF “has always been understood to authorize the use of force for the related dual purposes of helping to establish a stable, democratic Iraq and of responding, including through the use of force, to terrorist threats emanating from Iraq.” In theory, Soleimani and the other targets of the Jan. 3 strike could qualify as either, due to the Iran-backed PMFs’ history of undermining the rule of law in Iraq and engaging in acts of terrorism targeting U.S. personnel. Moreover, just as the 2002 AUMF authorizes the use of force in Syria where doing so furthers its purpose, it might also authorize the use of military force in other neighboring countries, like Iran.

If the administration were to determine that Iran or its affiliates fall within the scope of either AUMF, this would mean that, in the executive’s view, Congress has authorized the use of all “necessary and appropriate” force against them. This sets no real limits: The Trump administration may choose to pursue a full-fledged military campaign against each, regardless of how long it lasts or how many U.S. troops it places in harm’s way. Nor would any such conflict be subject to the War Powers Resolution’s 60- to 90-day limitation.

That said, doing so may involve substantial political risk. Both authorizations are almost two decades old, and the current situation was clearly not within Congress’s contemplation when it enacted either of them. Pushing the envelope here may encourage efforts to revoke the AUMFs or cut off funding for contested activities.

In recent congressional correspondence, the Trump administration has also posited another, somewhat narrower interpretation of the 2001 and 2002 AUMFs. Specifically, it has argued that, under a theory of “collective self-defense,” both AUMFs authorize U.S. military action in defense of U.S. and partner forces who are themselves engaged in any activities under the AUMFs, essentially allowing the United States to protect them from attacks by third parties who would not otherwise be covered by the statutes. The Trump administration has already deployed this logic in Syria, where it’s repeatedly taken military action to help local partners in the counter-Islamic State campaign to repel attacks by the Assad regime and its allies. During a Dec. 30 briefing, an unidentified State Department official suggested that the Trump administration may have similarly relied on collective self-defense to justify the Dec. 29 airstrikes. The same may also be true for the Jan. 3 strike.

If so, however, this would be in serious tension with how the Trump administration has told Congress it intends to invoke such collective self-defense. In prior correspondence, the Defense Department has assured Congress that this authority “permits U.S. forces to defend partners forces from attack or an imminent threat of attack with necessary and appropriate force” but that “[s]elf-defense is not a deliberate, offensive use of force ... [just] a reaction to an attack or imminent threat of attack.” Neither the Dec. 29 nor Jan. 3 strike fits neatly within this description, as both look like premeditated acts aimed at more than just repelling ongoing attacks. However, if Pompeo’s assertion that there was a threat of an imminent attack proves to be true—and killing Soleimani was the only reasonable means of preventing that attack—reliance on this theory maybe more credible.

Other Issues

Two other domestic legal issues have come up in the context of the Suleimani strike: the presidential policy banning assassinations and whether Trump was obligated to inform Congress of the operation in advance. While neither imposes meaningful domestic legal restrictions on the president, both warrant brief discussion.

President Gerald Ford adopted the first presidential ban on assassinations in 1976, as part of a set of reforms to the intelligence community following the Church Committee hearings. The current version of the ban is codified in Part 2.11 of Executive Order 12333, as subsequently amended, and states simply, “No person employed by or acting on behalf of the United States Government shall engage in, or conspire to engage in, assassination.” What constitutes assassination, however, is left undefined. Subsequent presidential administrations have reportedly interpreted it to mean primarily unlawful killings, which would not necessarily reach valid targeting decisions during armed conflicts. Notably, while most of these interpretations are not public, we do know that the Obama administration’s OLC concluded that “killings in self-defense are not assassinations” in the context of drone strikes against al-Qaeda-affiliated targets in Yemen—a conclusion that likely bears on the decision to kill Soleimani. In addition, as the ban is a presidential policy, it is subject to rescission and amendment by subsequent presidents. In short, as interpreted and applied by various presidents, the assassination ban does not clearly prohibit or otherwise limit the Soleimani strike.

Nor does Trump appear to have been under a specific obligation to inform Congress of his decision to pursue the Jan. 3 strike, either in advance or after the fact. The War Powers Resolution does require that the president consult with Congress “in every possible instance” before introducing U.S. armed forces into hostilities, but questions about both the vagueness and the constitutionality of this requirement have rendered it largely ineffective. Congress has enacted more specific reporting requirements in relation to covert action and sensitive military operations that seek to capture or kill specific individuals, but both provide exceptions to advance notification requirements in extenuating circumstances, which the opportunity to strike Soleimani may have presented. More importantly, the reporting provision for sensitive military operations—which most likely applies to the Soleimani strike, as the operation appears to have been conducted by the Defense Department—expressly excludes “any operation conducted within Afghanistan, Syria, or Iraq” from its scope. Hence, while consulting with Congress in advance may have been advisable and consistent with past practice for such significant operations, the Trump administration was not clearly under a legal obligation to do so.

What Now?

For many observers, the prospect that the president has such free reign to use military force overseas—even in ways that are in tension with the executive branch’s prior positions—is likely to be disconcerting. Yet this is the direction in which the U.S. legal system has gravitated over the past century, thanks to a combination of executive aggrandizement, judicial reticence and congressional abdication. Those with serious misgivings over the president’s decision to pursue the Jan. 3 strike—sentiments I share—may have hoped that the law provided some means of checking the president’s authority in the future. But the law is not a solution for bad policy or poor decision-making. For better or worse, the United States has chosen to vest its president with extensive unilateral authority to use military force—no matter who holds that office or how that authority is used.

That said, this arrangement of authorities is not immutable. Even executive branch lawyers have generally acknowledged that Congress has substantial authority to set limits on the president’s authority to use military force through statutes. And there is reason to believe that federal courts may feel more compelled to enforce such limits through judicial review if they are enacted with clarity.

Ironically, a majority of the members of the current Congress voted to do exactly that this past summer in regard to Iran. Motivated by concerns over escalating tensions with Iran, both the House of Representatives and 50 members of the Senate supported an amendment to the most recent National Defense Authorization Act (NDAA) that would have prohibited the use of funds for military operations against Iran—most likely preventing the Jan. 3 strike, or at least forcing the Trump administration to rely on narrower and more contentious legal grounds. That legislation failed because it did not secure the 60 votes in the Senate necessary to proceed. But future legislation might be more successful, especially if the Trump administration’s policy decisions and related legal justifications trigger a backlash.

That said, any freestanding legislation would have to contend with Trump’s likely veto, which would require support from two-thirds of both chambers to override. Alternatively, Congress could try to attach such legislation to an omnibus bill like the NDAA that would be more difficult for Trump to veto—except that Congress has just recently approved most such bills for the coming year, meaning another such opportunity may not readily present itself for the next 12 months. These challenges underscore Congress’s limited ability to rebuke presidential decisions in the war powers space after the fact and, thus, the importance of setting up anticipatory legislative frameworks if it wishes to check presidential actions in this space.

But the primary check on presidential war powers decisions comes from the political process. While presidents may rely on an unpersuasive legal justification, doing so can still have political ramifications, both for them and their supporters in Congress. Though indirect, imposing electoral costs in this manner can be an effective way to curb presidential overreach in the long run. And until a sufficient majority of Congress comes to support corrective legislation, electoral rebuke may be the only remedy truly available.