Michael Byers teaches global politics and international law at the University of British Columbia.
Remember when U.S. President Donald Trump asserted that he did not need international law – that the only limit on his global powers was his own morality? That attitude reflected a time, just three months ago, when Mr. Trump felt all-powerful. Rules were for wimps. The views of allies could be brushed aside.
But now, as the war in Iran drags into a third month, Mr. Trump’s position has become more complicated. He desperately wants allies to help him open the Strait of Hormuz, and some of those allies – notably France and Britain – care about international law.
Enter Reed D. Rubinstein, a corporate lawyer and Trump supporter. In May, 2025, Mr. Rubinstein was appointed legal adviser at the State Department, making him the senior international lawyer in Washington, D.C.
Last week, Mr. Rubinstein released a letter making the legal case for the attack on Iran launched in February, 2026. Though the letter does not deal with the conduct of the conflict – only the initiation of the bombing campaign – it would not have been easy to write. International law allows for only two exceptions to the prohibition on the use of force, and the first – an authorization from the UN Security Council – was never pursued by the Trump administration. As a result, Mr. Rubinstein had to base his argument on the second exception, the right of self-defence, which is recognized in the UN Charter but subject to the customary international law requirements of necessity and proportionality.
In June, 2025, the Trump Administration argued it had met those criteria when it attacked Iran’s nuclear enrichment facilities, because they posed an “imminent” threat. That claim was questionable, but for present purposes, what matters is that, after those strikes, Mr. Trump declared that “Iran’s key nuclear enrichment facilities have been completely and totally obliterated.”
This meant that Mr. Rubinstein could not make the same argument this year. His letter concedes this, stating that “the United States does not rely on a theory of imminence to justify its actions in this case” (though Mr. Trump’s initial remarks on Feb. 28 suggested otherwise.)
Instead, Mr. Rubinstein reached for a more dubious argument, asserting that the current bombing campaign “is only the latest round of an ongoing international armed conflict with Iran.” “Beginning with its founding in 1979,” he writes, “the Islamic Republic of Iran has regularly attacked the United States, its interests, and its allies, including but not limited to Israel, directly and through proxies.” Mr. Rubinstein continues the argument by asserting that “if a conflict has not ended, then it must be ongoing,” and that, if a conflict is ongoing, there is “no requirement to continually reassess” the principles of necessity and proportionality that are central to the right of self-defence.
In other words: it does not matter whether it is necessary to the defence of the United States to continue the bombing campaign against Iran into a third or fourth month, or indeed indefinitely. All that matters is that the initiation of the war – in 2005, or even way back in 1979 – was necessary.
Clearly, this is not an argument for self-defence, but rather for a claimed right to engage in forever wars. And that is a right that, if accepted by other countries, would only lead to chaos.
The world is full of unresolved conflicts. Pakistan has repeatedly claimed self-defence along its border with India; can it legally launch missiles at New Delhi? The Philippines has repeatedly claimed self defence against China in the South China Sea; can it legally launch missiles at Beijing? According to the BBC, the Trump administration is considering supporting Argentina in its centuries-long dispute with Britain over the Falkland Islands. Can Argentina invade again?
Fortunately, Mr. Rubinstein’s argument fails to account for certain public statements by Mr. Trump, including a June 23, 2025, declaration on social media that the war with Iran was coming to an “official END”. Later, in October, 2025, the State Department listed the war with Iran as one of the eight that the “President of Peace” had brought to an end. Consistency matters when it comes to legal arguments. Mr. Trump might wish it otherwise, but you can’t have your cake and eat it too.
