U.S. Secretary of State Marco Rubio has offered a striking explanation for why the United States attacked Iran: Washington, he said, “knew that there was going to be an Israeli action,” anticipated that Iran would retaliate against U.S. forces, and therefore hit first to reduce American casualties. The formulation is not only politically convenient; it is conceptually confused. It implies that the United States acted because Israel was going to act—yet also insists that the operation “needed to happen,” as Rubio put it, regardless. That is, the argument simultaneously portrays America as reluctantly reacting to an ally and decisively pursuing...