President Obama’s explicit call for Syrian President Bashar al-Assad to step down must have sparked consternation in at least three Middle Eastern capitals today – within the presidential palace in Damascus, the headquarters of Hezbollah in Beirut, and among the mullahs of Teheran.

Several hours after President Obama announced a fifth round of sanctions on Assad’s regime and Secretary of State Hillary Clinton echoed Obama in demanding that Assad stop slaughtering his people and “get out of the way,” the official website of the Syrian government made no mention of their declarations. It continued featuring articles about the joys of shopping in Damascus and an upcoming desert festival in the ancient city of Palmyra.

The Iranians were also initially silent about Syria, the Islamic republic’s most important Arab ally and neighbor. So, too, was Hezbollah, or the “Party of God,” the Iranian-allied Shiite militants who dominate Lebanon’s fractious government and whose arms shipments depend on transit routes from Iran thru neighboring Syria.

But the real address of the Obama administration’s belated announcement is the Syrian opposition. Both President Obama and Secretary Clinton stress that it is, as the president said, “up to the Syrian people to choose their own leaders.” Syrian regime opponents have repeatedly told Washington, Obama and Clinton say, that they do not want foreign military intervention in their struggle to oust their ophthalmologist dictator, who has already killed more than 2,000 unarmed civilian protesters in cities throughout Syria. Others say the toll is far higher. Ammar Abdulhamid, a prominent Syrian opposition figure, estimates that as of last week, the regime had killed 2,675 people, including 158 children, and detained 16,000. Another 4,382 people are missing, he says.

So a key test of the impact of Obama’s declaration is likely to come this Friday and in ensuing weeks: will Syrians continue risking death and injury by pouring out in the streets to demand Assad’s ouster? Will they continue to challenge Assad peacefully? Will the “Local Coordination Councils,” regime opponents who have been rallying support and keeping track of the cost of the mayhem, be able to form a coherent political opposition?

Even prior to today’s declaration from Washington, Assad had been battling the toughest challenge to his regime since he inherited power from his even more brutal father, Hafez, 11 years ago. But rather than step aside or yield to calls for political reform, he has sent an army dominated by his minority religious clan, the Alawites, to brutally suppress the revolts -- killing, arresting, and torturing unarmed protesters and using his diplomats abroad to intimidate their families, as documented by an excellent article this week in The Wall Street Journal.

Another key focus will be Turkey, whose foreign minister, Ahmet Davutoğlu, recently visited Damascus to give his neighbor, and Turkey’s largest trading partner, 14 more days to implement reform.

Mr. Davutoglu is the father of the Turkish foreign policy known as “zero problems with neighbors," which has centered on using Turkey's growing leadership role in the Middle East to become indispensible to America by improving relations with Iran and Syria and helping to broker Arab-Israeli peace talks. But this policy has been upended by Assad’s brutality and Turkey’s inability to persuade Assad to accommodate his critics.

So Obama, argues Tony Badran, a veteran Middle East watcher at the Foundation for Defense of Democracies, decided he had to call openly for regime change, while Turkey has continued “to hold out hope for a reform program led by Assad, precisely… to preserve its own influence as an intermediary between Iran, Syria, and Washington.” Washington must now put extra pressure on Ankara to hold Assad accountable for his regime’s crimes.

What else can be done? That is unclear.

Nor is it clear who would take power in Syria in the unlikely event that Assad decided to step down.

But many veteran diplomats in the region think that Washington’s declaration, though it has put the United States on the “right side of history,” as administration officials are fond of saying, will have little direct impact on the ground in Damascus. Assad, one veteran Arab diplomat notes, has no reason to relinquish power and every reason to try to hang on. A United Nations panel in Geneva announced today, for instance, that it would refer the Syrian regime to the International Criminal Court in the Hague to investigate reports of the regime’s war crimes.

The White House is now also likely to step up efforts to delegitimize the Syrian regime through sanctions and other forms of international disapproval.

The sanctions announced Thursday bar Americans from engaging in any financial transactions with Damascus, and especially with Syria's oil industry. It is urging the European Union, which buys about 90 percent of Syria's oil exports, to stop importing, and take other steps to strangle the regime financially.

Finally, argues David Schenker, of the Washington Institute for Near East Policy, the administration must continue trying to persuade Russia to stop selling arms to the Syrian regime. That will not be easy, says Schenker. Yesterday, a leading Russian arms exporting organization said it would continue making such sales. The diplomatic road ahead seems laden with such land mines.

Judith Miller is a writer and author. She is a Fox News contributor and Manhattan Institute scholar.