The decision by Russia and China to veto a U.N. Security Council resolution to impose sanctions on the brutal regime in Syria is, at most, a hollow victory for President Bashar Assad.

Russian officials say they opposed the measure for fear that it would lead to regime change, possibly with the assistance of Western military forces, as in Libya. But given the events on the ground in Syria, the veto appears likely only to ensure that regime change comes through blood and chaos, not diplomacy.

Mr. Assad obviously has no regard whatever for the suffering he has inflicted on Syria’s beleaguered civilian population.

While he insists that his stepping down would plunge the country into chaos and civil war, the truth is the longer he stays, the deeper the crisis enveloping his country will become.

Even so, Russia and China are refusing to pull the plug on this brutal dictatorship, and now the U.S. and its allies must prepare for the worst, including the possibility that a sudden disintegration of the regime could allow some al-Qaida-backed elements to get their hands on Syria’s large stockpile of chemical weapons.

Though the Obama administration has been right to be cautious about intervening militarily in Syria’s upheaval, the possibility that radical Islamists might use such weapons to attack the West lead the president to consider a narrow but prompt and decisive U.S. military response.

Reluctant as the administration has been to jump into another Mid-eastern war, such an action by the U.S. and its Western allies would be less destabilizing than similar action by Israel, and it might be the only way to head off what Secretary of Defense Leon Panetta described on Wednesday as the most dangerous scenario imaginable for a regime that is rapidly spinning out of control.