The governments of France, Saudi Arabia and Jordan, which at times in the past have been supportive of Assad, are all said to have concluded that the Assad regime cannot survive the repercussions of the violence it loosed on Syrian protesters in recent weeks. Turkey, too, which initially seemed eager to broker a compromise for Assad, also appears less supportive.

France, which a decade ago was Assad’s champion, is now said to have concluded that major powers, including Paris and Washington, should signal publicly that it is time for Assad to leave office. But the White House Tuesday appeared to be weighing whether to make one last attempt at brokering the kind of reforms that Assad has said for years he wanted but has never implemented.

The United States initially held back from personally sanctioning Assad, deciding instead to concentrate its fire on the hard-liners around him. Secretary of State Hillary Clinton said Tuesday, however, that the United States is preparing additional sanctions. Many U.S. analysts see Assad as having squandered any chance he had to be a credible reformer.

Israel, which seemed for a time to prefer “the devil we know” in Assad, has told the United States it doesn’t endorse this argument any longer.

The challenge for policymakers as Assad’s power fades is to find a transition process that can avoid a Libya-style military confrontation. The Syrian version of regime change could be far bloodier because of the deep enmity between Sunnis and the Alawite minority that has governed since Assad’s father, Hafez al-Assad, seized power in a coup in 1971. Already, in mixed cities such as Latakia and Homs, there is said to have been ethnic killing that could presage a much wider pattern of violence. Violence in Syria could also spill over into Lebanon.

Peaceful change is difficult in Syria in part because generations of harsh Baath Party rule have stunted the growth of political figures outside the ruling circle who might now play a role in a transition. The firepower for the movement to oust Assad, by most accounts, has come from the Muslim Brotherhood, not from civil society activists as was the case in Egypt’s Tahrir Square revolution.

The big danger is that the Assad regime will decide to hunker down and make a grim last stand. That certainly was the tone of recent comments from Rami Makhlouf, Assad’s cousin and a leader of the hard-line faction within the Assad clan.

     Makhlouf warned in an interview with the New York Times last week: “We will not go out, leave on our boat, go gambling, you know. We will sit here. We call it a fight until the end. . . . They should know when we suffer, we will not suffer alone.”