Mr. Obama’s problem is that Mr. Khamenei could only have chosen Ahmadinejad because he does not want friendly talks with the U.S. He evidently calculates that without the ideology of “anti-Americanism” the regime would collapse. He is right.

Certainly religious support cannot be enough anymore. Too many high-ranking clerics, including Grand Ayatollahs Hosssein Ali Montazeri and Yusef Saanei, now publicly oppose the regime. Nor can Persian nationalism serve as the prop: Its chief target is the despised Arabs, which is problematic, as the regime keeps trying to be more Arab than the Arabs in its hostility to Israel. Yet this hostility is itself a problem internally because the regime’s generous funding of Hezbollah, Hamas and Islamic Jihad is extremely unpopular in Iran. Only anti-Americanism is left, and Mr. Khamenei will not let Mr. Obama take it away.

Unless Iran’s politics change, Mr. Obama’s policy will fail.