Nearing midnight.

THE U.N. Security Council's deadline for Iran to stop enriching uranium has passed, but the centrifuges at Natanz are still spinning. That Iran defied the deadline should surprise no one. What does surprise us is that the president who swore he would not "permit the world's most dangerous regimes to threaten us with the world's most destructive weapons" does not show more urgency in fulfilling that pledge.

The U.S. is holding off on seeking sanctions through the U.N. while European negotiators make a last-ditch effort to sweet-talk the mullahs into pacifism. That might be worth a try if they hadn't spent the last four years trying it. Coming now, it's simply a display of weakness. If the Security Council were worth its name, Iran would have seen, at the moment of the deadline's expiry, a resolution authorizing tough punitive measures. Instead, it sees a Security Council incapable of anything but fruitless and feckless diplomacy, and a United States apparently resolved to this irresolution.

An oil blockade could hurt the regime, but it is also a diplomatic impossibility. And Russia and China will refuse to support even modest sanctions. Russia in particular has hundreds of millions of dollars at stake in the construction of an Iranian nuclear reactor. Both nations promised the U.S. that they would back sanctions if Iran failed to halt enrichment--and show not the slightest intention of keeping their word.

We would be fools to take comfort in a recent International Atomic Energy Agency report suggesting that Iran's enrichment activities are proceeding slowly and producing uranium of a quality too low for weaponization. Given enough time, the regime will build its nukes. The paramount mission of the Bush administration in its remaining two years should therefore be twofold: to keep the mullahs from going nuclear, and to speed their fall from power. Unfortunately, these objectives do not admit of a single solution. We should redouble our aid to the Iranian democracy movement, but we cannot assume that the revolution will come before the bomb.

Stopping the bomb will require us instead to hasten the diplomacy to its inglorious denouement and think very seriously about our military options. A preemptive air strike is a nasty thing to contemplate. The mullahs could retaliate against us in Iraq. They could sabotage tanker shipments in the Persian Gulf. They could back terrorist attacks on U.S. soil. But the alternative--a nuclear Iran--is vastly worse. Even if the mullahs never used their arsenal, its simple existence would deal a catastrophic blow to U.S. interests. It would effectively give Tehran a veto over U.S. military action in the region. Since the nuclear facilities are protected by the Revolutionary Guard--rabid ideologues who operate with a high degree of autonomy--a weapon could conceivably be transferred to terrorists without the central government's okay. And an Iranian bomb would likely produce a regional arms race and multiply the number of Middle Eastern nuclear powers. This too would raise the likelihood of a nuclear weapon's falling into terrorist hands; and by making it harder to determine where a detonated bomb had originated and retaliate against the guilty party, it would give the jihad that much more incentive to push the button.

Bush has made forfending that possibility his presidency's raison d'etre. We believe he means it. But we wonder how much longer he will wait before abandoning "solutions" that are anything but.