A member of the Islamist Syrian opposition group Ahrar al-Sham...

A member of the Islamist Syrian opposition group Ahrar al-Sham fires against a militia set up to protect Kurdish areas in Syria during clashes in the countryside of the northern Syrian Raqqa province. (Aug. 25, 2013) Credit: Getty Images

A U.S. led military strike in Syria appears inevitable now that it's clear President Bashar Assad crossed President Barack Obama's "red line" by using chemical weapons against his own people.

Assad's brutality and brash defiance of international law has left the United States with nothing but bad options. It can punish Assad for his unconscionable actions, or it can stand idly by and do nothing. It's a dreadful choice.

If Obama does nothing to back up his rhetoric, other despots will be emboldened to use nasty, prohibited weapons against civilians, and U.S. threats of reprisal will lose all credibility. But the limited airstrikes the administration is talking about won't change the course of the Syrian civil war.

Obama shouldn't have drawn this line in the sand last August, when he said "a red line for us is we start seeing a whole bunch of chemical weapons moving around or being utilized. That would change my calculus." One painful lesson learned here: He should avoid such ultimatums in the future.

If the United States can't in good conscience stand by and do nothing in Syria, a limited airstrike would be the least bad option. Though the chemical attack has given Obama strong ground to respond, the United States shouldn't go it alone. Obama should assemble an international coalition to go along, including particularly some of Syria's Arab neighbors.

Cruise missiles fired on military targets could crater runways, disable planes on the ground, and degrade Syria's military command and control capabilities. None of that is likely to topple Assad. The administration said that the objective of retaliatory strikes would not be regime change.

That's just as well because the facts on the ground are complicated. The Syrian insurgents have militant Islamists in their ranks. Even if airstrikes did help drive Assad from power, whatever government comes next is unlikely to be a friend to the United States.

The red line Assad crossed last Wednesday wasn't just Obama's. It was drawn years ago by international law. It should be enforced by a community of nations.