President Donald Trump's threat against Iran marks a grave political and moral decline. Speaking about a possible expansion of the bombing campaign, he said that "a whole civilization will die tonight, never to be brought back again." That sentence does not sound like the language of a president discussing military objectives. It presents the possible result of American action as the destruction of a civilization. Once a president speaks in those terms, accusations of genocidal threat cease to be fanciful or polemical. He has introduced them himself. The legal point should be stated with care. A court would probably not treat this single statement as dispositive proof of genocidal mens rea. The Genocide Convention sets a high threshold. It requires specific intent to destroy, in whole or in part, a protected group as such...