WHEN THE SYRIAN regime lost control of the city of Hama last month, some Western experts concluded that President Bashar al-Assad would not attempt to restore his authority by force. Hama, after all, was the site of one of the most infamous massacres in the history of the Middle East — a 1982 assault ordered by Mr. Assad’s father that killed tens of thousands. Surely, the experts opined, the world has changed enough that the regime would not even attempt to repeat its extraordinary crime.

And yet that is what Mr. Assad is doing. Early on Sunday, army troops led by tanks launched an assault on the city of 800,000 from four directions, firing cannon and machine guns indiscriminately at the unarmed residents manning street barricades. Video clips posted on YouTube showed the tanks blasting at the minarets of mosques in a city known for its Sunni conservatism, while snipers picked off people on the streets.

The attack began on the eve of Ramadan, the Muslim holy month, and continued on Monday. It’s not known how many people have died; foreign journalists and other independent observers have been kept out of Hama. But Syrian opposition sources reported at least 55 deaths on Sunday, and by Monday some counts exceeded 100.

The attack reflects Mr. Assad’s desperation; the regime appears to see no way to save itself other than by waging war on the civilian population. But Mr. Assad clearly is also calculating that those who suppose that dictators can no longer get away with massacres are wrong. He has some basis for that conclusion: NATO may have intervened in Libya to prevent the slaughter of civilians by Moammar Gaddafi, but Western leaders have publicly and vehemently ruled out intervention in Libya. The U.N. Security Council has failed to speak out against Mr. Assad’s assaults on other cities, as has the Arab League.

Until recently, the Obama administration was still describing the solution to Syria’s crisis as negotiations between the regime and opposition. On Sunday President Obama, who has spoken in public about Syria only twice since the rebellion began in March, issued a statement saying he was “appalled” by the “horrifying” reports from Hama, “which demonstrate the true character of the Syrian regime.” It was not clear, however, what action, if any, the administration was prepared to take.

Mr. Obama promised that “in the days ahead, the United States will continue to increase our pressure on the Syrian regime.” But we have heard that before. On June 17, administration officials gave reporters a briefing in which they used those same words and talked about such measures as sanctions against Syria’s oil and gas sector and the referral of Mr. Assad and his collaborators to the International Criminal Court on war crimes charges. Nothing has happened since then. Is it any wonder that Mr. Assad thinks he can slaughter the people of Hama with impunity?