By Michael Rubin

Iranian President Mahmoud Ahmadinejad shrugged off Wednesday's U.N. Security Council resolutions, saying they "resemble used napkins that need to be thrown to the garbage can." Diplomacy has hit a dead end: President Obama bargained away everything just to win watered down sanctions.

OUR VIEW: On Iran, it's time to weigh what comes after sanctions

Spinning centrifuges run down the clock. When Obama asked Iran to unclench its fist, it lacked the uranium to build a bomb. Today, it has enough for two.

If President Obama does not act quickly and unilaterally to paralyze Iran's banking sector and stop the gasoline imports the Islamic Republic needs to survive, he will be left with a stark choice: Launch a military strike or let Iran get the bomb.

Containment will not work: Obama is unprepared to deploy the forces, build the bases, or spend the billions of dollars that containment would cost. Regardless, with an intercontinental ballistic missile capability by 2015, the Islamic Republic could leapfrog any containment. Nor will Arab states and Israel accept the promise of a U.S. nuclear umbrella after Obama casts aside a decade of assurances that the United States would never tolerate a nuclear Iran.

The Islamic Republic cannot be trusted with nuclear weapons. Ordinary Iranians are moderate, but the Islamic Revolutionary Guard Corps— the most radical group in the country — would control the arsenal. Deterrence will not bring security: During the Cold War, luck was as important as "Mutually Assured Destruction" in averting nuclear Armageddon. The Iranian regime may not be suicidal, but if it believes its days are numbered by a repeat of last year's popular uprising, the Guards might just launch weapons at Israel or America to fulfill ideological desire.

U.S. military strikes should be a last resort, but they can set the Islamic Republic's nuclear program back years. Any strike, however, requires destroying not only Iran's nuclear facilities, but also its command-and-control and anti-aircraft capability. An airstrike can also expose what the CIA does not know: After the first sorties, U.S. intelligence need only to look where the Iranian military guards are.

The cost of any strike will be high: The Iranian people will rally around the flag, the price of oil will spike (but eventually decline) and Tehran will unleash a wave or terror. But, should Iran gain the bomb, the international community will suffer similar consequences.

If the United States prepares now, Iran may reconsider the cost of defiance. Throughout the 1980s, Ayatollah Ruhollah Khomeini said he would fight Iraq until victory. In 1988, as the cost became clear, he agreed to a cease-fire, saying it was like "drinking from a chalice of poison." President Obama, it's time to hand Ahmadinejad the cup.

Michael Rubin is a resident scholar at the American Enterprise Institute.