As Stanford Law’s Allen Weiner, an expert in international law, said of Trump’s justification for the attack: “There is a strong moral valence to the president’s remarks; he referred to the Iranian regime as a ‘vicious group of very hard, terrible people’. The president also cited a number of historical grievances against Iran, going back to the 1979 Tehran embassy hostage-taking and Iran’s support for anti-American militias during the post-2003 American occupation of and subsequent military presence in Iraq.”

However, Weiner goes on to explain that international law is explicitly crafted to outlaw exactly this kind of “just in case” attack.

“My judgment is that the attack was quite clearly illegal,” he said.

A general danger, Weiner said, or the possibility that Iran may at some point in the future acquire nuclear weapons, was not enough without an explicit threat.