Third, the president is ideologically committed to a world without nuclear weapons. If Iran gets the bomb, it will set off an arms race in the world’s most volatile region. At the very least, Saudi Arabia and Turkey will seek nuclear weapons. It would mark a bitter defeat for Obama to have inadvertently overseen the greatest expansion of the nuclear arms club in recent history.

Finally, the president has a deep understanding of Jewish history, and is repulsed by Iranian anti-Semitism. He doesn’t want to be remembered as the president who failed to guarantee Israel’s existence.

This isn’t to say that Obama has decided to use whatever means necessary to stop Iran. (He faces opposition in the Pentagon, for one thing, though the U.S. military has much greater capabilities than Israel.) Nor is a U.S. strike something desirable, even if done in concert with Western allies. It’s far better for the Iranians to be persuaded through other means to stop their nuclear program.

But numerous Israeli officials have told me that they are much less likely to recommend a preemptive strike of their own if they were reasonably sure that Obama was willing to use force. And if Iran’s leaders feared there was a real chance of a U.S. attack, they might actually modify their behavior. I believe Obama would use force — and that he should make that perfectly clear to the Iranians.