THE failure of diplomacy to stop Iran’s nuclear program became obvious this week, when President Mahmoud Ahmadinejad revealed the installation of 6,000 new centrifuges at the country’s main uranium enrichment complex. His announcement was accompanied by the now customary assertion that outsiders can do nothing to stop Iran from fulfilling its nuclear destiny.

Once, not so long ago, this kind of boast would elicit clear American declarations that Iran would never be allowed to develop nuclear weapons. Everything, President Bush would say ominously, is on the table. This time he has been quiet. I wish I believed that it is the quiet before a storm of laser-guided action. It seems more likely that it is the abashed silence of an American president whose bluff has been called in front of the entire world.

Washington’s performance should concern anyone who cares about long-term American influence in the Islamic world. But for Israel (and Israel’s supporters), this is an urgent problem. It is Israel, after all, that has been set by the Iranian leadership as the target for annihilation.

In response to the news from Iran, some supporters of Israel have started to suggest that the failed efforts at prevention be replaced by assured American deterrence: any Iranian nuclear attack on Israel would be treated as an attack on the United States. Charles Krauthammer, a Washington Post columnist, recently referred to this as “the Holocaust doctrine.”