National Security Adviser Robert O’Brien told reporters that the killing was justified under the 2002 law Authorization for Use of Military Force Against Iraq, which was passed to permit the president to act to address threats posed by Iraq. Relying on the law would require a conclusion that the threat from Soleimani, an Iranian government official, was posed by Iraq. In other words, relying on the law is as good as admitting there is no legal basis. Vice President Mike Pence also asserted a false connection between Soleimani and the 9/11 attacks, perhaps in an effort to suggest that the strike could fall under the 2001 Authorization for Use of Military Force. Those claims have been widely discredited, and several members of the Senate earlier expressed skepticism that the 2001 law authorized action against Iran.

Without any more solid legal authority to cite, the Trump administration seems to have turned to the claim that it was acting in self-defense. Though the administration has yet to provide any clear explanation for the legality of the strikes, it has offered various clues that the central justification is the president’s right to engage in self-defense on behalf of the United States. The Department of Defense issued a short statement suggesting that the attack was justified as an act of defense “aimed at deterring future Iranian attack plans.” Secretary of State Mike Pompeo later more forcefully claimed that the strike was aimed at disrupting an “imminent attack.”

This claim—were it true—could solve the administration’s domestic and international legal problems at once. Both the U.S. Constitution and the UN charter include an exception for self-defense. Under Article II of the Constitution, the president may act to respond to imminent threats to the nation. The original idea was that there may be times when it is impractical or impossible to convene Congress—something that was especially true when communication and travel could take weeks. In such cases, the president would not be prevented from taking necessary action to defend the nation until Congress could be convened. The UN charter, which prohibits a state from unilaterally resorting to the use of force against another state, also allows for an exception in cases where the state has been the subject of an armed attack or, most experts agree, will imminently be subject to such an attack. In both cases, the exception is narrow: The threat must be so extreme and imminent that it would be unreasonable to seek the necessary approvals before taking action to defend the country.

New reporting from The New York Times, however, concludes that “the evidence suggesting there was to be an imminent attack on American targets is ‘razor thin.’” A U.S. government official reportedly described the claim that Soleimani was planning an attack “that could kill hundreds” as “an illogical leap.” In short, it does not seem there was any imminent threat justifying unilateral action by the president.