Trump Is on Shaky Ground in Legally Justifying a Strike on Iran

President Donald Trump implied in his State of the Union address this week that his justification for another military attack on Iran was ensuring that the “the world’s number one sponsor of terror” will never have a nuclear weapon.

In theory, that’s a valid legal justification for a preemptive, proportionate use of force, but the facts don’t support the conclusion that Iran is close enough to getting deliverable nukes such that US military action now would be lawful.

Trump didn’t hint at other reasons for attacking Iran in his speech. That’s a relief because there are no other viable legal justifications. For starters, US forces and bases in the Middle East haven’t been subject “to an escalating series of attacks in preceding months by Iran and Iran-backed militias.” Those attacks provided a reasonable self-defense basis for the Jan. 2, 2020, US drone strike in Iraq that killed Major General Qasem Soleimani, head of Iran’s Quds Force, the principal architect of those attacks.

The Soleimani strike was limited and proportionate: detonation in Iraq by a single unmanned drone with no risk to US servicemembers and no civilian casualties. But self-defense doesn’t apply this time because Iran hasn’t attacked US forces since launching missiles against US bases in Iraq and Qatar on June 23, 2025, in retaliation for the US and Israeli bombing of Iranian nuclear facilities. Iran gave notice to the US of the strikes in advance and there were no US casualties.

There are five potential reasons other than self-defense: 1) finishing off Iran’s nuclear-weapons program, including any weapons-grade enriched uranium; 2) averting a humanitarian crisis given credible evidence that thousands of unarmed civilians have been killed; 3) destroying Iran’s ballistic-missile program, which poses threats to Israel, US, and allied bases and forces in the region; 4) degrading Iran’s capacity to support proxy forces such as Hamas, Hezbollah, the Houthis, and other terrorist groups; and 5) regime change by taking out Ayatollah Ali Khamenei.

The last three reasons are plainly unlawful. One country doesn’t have the right to use its armed forces to kill another country’s leader, stop it from arming and supporting its proxies, or destroy its conventional weapons. If, in 1981, Soviet armed forces had bombed the US Navy on the 40th anniversary of the attack on Pearl Harbor, assassinated President Ronald Reagan, or fired missiles at the Pentagon to stop aid to Nicaraguan contras and Afghan mujahedeen, everyone in the US and around the world outside the Soviet bloc would have condemned the act as a flagrant breach of Article 2(4) of the UN Charter.

Although it doesn’t offend the UN Charter for one country to use armed force to stop genocide or mass killings in another, the situation in Iran doesn’t yet seem to be at the level of a humanitarian crisis.

There’s no evidence that the Iranian regime is exterminating a religious group like the Nazis killed Jews or that it’s perpetrating a massacre like Serbia of Muslims at Srebrenica in 1995 or the Hutus of Tutsis in Rwanda in 1994.

There is evidence of widespread, indiscriminate killings of protesters, but those killings seem to have abated recently. And, as I wrote in 2014, a country may use force to stop a humanitarian crisis in another country only when there is “clear and convincing evidence of genocide, massacre crimes against humanity, or the lethal use of weapons of mass destruction against civilians.” As important, the use of force to stop a humanitarian crisis must be limited to stopping the genocide, massacre, or use of weapons of mass destruction—not regime change.

A preemptive strike on another country to stop it from acquiring or using nuclear weapons would be lawful, but it’s the toughest issue in the law of justifications for use of force. In 1953, President Dwight D. Eisenhower released NSC 162/2, which addressed the reality that the Soviet Union had the hydrogen bomb and was rapidly developing its nuclear weapons capabilities. NSC 162/2 didn’t rule out first use of nuclear weapons, presupposing the legality of a US nuclear first strike.

In 1962, air strikes on sites in Cuba where Russian nuclear missiles could be positioned was an option that President John F. Kennedy seriously considered but rejected. But Kennedy didn’t reject the use of force because he thought US or international law prohibited it. Rather, he believed a naval quarantine was the better policy option.

In 1981, Israeli warplanes destroyed an Iraqi nuclear reactor under construction at Osirak, anticipating its future use in a nuclear-weapons program. In 1994, President Bill Clinton almost ordered military strikes on the Yongbyon nuclear reactor and other nuclear facilities before cutting a deal with North Korea. And in 2017, Trump seriously weighed military strikes after North Korea had tested a long-range ballistic missile before agreeing to summit meetings with North Korean leader Kim Jong-un.

Finally, and most relevantly, in June 2025, the US and Israel commenced an intensive 12-day bombing campaign against three nuclear facilities in Iran called Operation Midnight Hammer. Trump claimed the strikes had “completely and totally obliterated” the targets, and the Pentagon assessed that Iran’s nuclear-weapons program was likely set back two years.

For a second air strike to be legally justified, either the initial assessments must be wrong or the Iranians have managed to recover the enriched uranium and rebuilt the destroyed facilities in the past several months to the point that they will imminently have nuclear weapons.

However, the Trump administration hasn’t officially walked back the initial damage assessments. And there is no publicly available official information indicating that Iran has rebuilt their nuclear-weapons program or salvaged enough super-enriched uranium from the bombed-out sites to do so.

The bottom line is that Trump’s claim that Operation Midnight Hammer was successful in achieving its objective undermines the case that a second, possibly larger military attack is lawful. Under international law, it wouldn’t be necessary or proportionate to take out Iran’s nuclear-weapons program because that program has already been “obliterated.”

And from a US law perspective, Iran’s public statements indicate that it won’t be as mild in the retaliatory use of force as it was in June 2025. That substantially increases the prospect of a prolonged regional conflict amounting to a war that would require Congress’ buy-in to be constitutional.

This article does not necessarily reflect the opinion of Bloomberg Industry Group, Inc., the publisher of Bloomberg Law, Bloomberg Tax, and Bloomberg Government, or its owners.

Author Information

Thomas H. Lee is a professor at Fordham Law School and author of the forthcoming book, “Justifying War.” He was also a senior Pentagon lawyer in the first Trump administration and a US naval cryptologist.

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