President Barack Obama's call for Syrian President Bashar Assad to resign didn't come as quickly as critics on the right and the left had demanded.

But administration officials insisted they needed time to build an international consensus that could help push Assad out.

For weeks, as the regime intensified its violent crackdown against pro-democracy protesters, Obama and other administration officials issued only vague statements to express their displeasure, saying Syria "would be better off" without Assad. When news reports suggested the U.S. was about to call for his ouster, U.S. officials indicated publicly there was no need to up the ante.

"I happen to think where we are is where we need to be, where it is a growing international chorus of condemnation," Secretary of State Hillary Clinton said Tuesday.

But on Thursday, Obama called explicitly for Assad's exit, and Clinton echoed his message on national television.

"The future of Syria must be determined by its people, but President Bashar al-Assad is standing in their way. His calls for dialogue and reform have rung hollow while he is imprisoning, torturing, and slaughtering his own people," Obama said in a written statement Thursday morning.

"He has not led. For the sake of the Syrian people, the time has come for President Assad to step aside."

Afterward, the White House seemed eager to dispel perceptions that the timing of Obama's action fits an emerging Republican critique that the president prefers to "lead from behind" - the phrase an unnamed Obama adviser used to describe Obama's foreign policy in an interview with The New Yorker earlier this year.

Indeed, Republican presidential candidate Mitt Romney struck just such a note in his response to Obama's call.

"It has taken President Obama far too long to speak out forcefully against Assad and his vicious crackdown in Syria," the former Massachusetts governor said in a statement. He said the administration's initial response to the Syrian unrest "had the effect of emboldening Assad and discouraging the dissidents."

In a conference call with

reporters, senior administration officials said Obama discussed calling for Assad's exit on Aug. 5 in conversations with French President Nicolas Sarkozy and Chancellor Angela Merkel. He settled on doing so by Saturday, when he spoke with British Prime Minister David Cameron. The European leaders issued a joint statement Thursday demanding that Assad quit.

"We steadily and systematically worked to build concerted international pressure," said one U.S. official, who spoke on the condition of anonymity in a White House-organized conference call with reporters. "The international chorus of condemnation in calling for Assad to go deepens his isolation."  

Some human rights activists endorsed Obama's measured approach even as they conceded they find it frustrating at times.  

"This White House is meticulous, not impulsive," said Tom Malinowski of Human Rights Watch, who had been privately urging U.S. officials to make an explicit call for Assad's exit. "I often find myself impatient with them because of that approach, but in the end I think it makes much more sense. They've done it in a way that there's going to be far more support from the Europeans and others in the region and be accompanied by actions that will make Assad pause more. ... I'm willing to wait a week or two to make these kinds of steps more meaningful."  

Malinowski said some countries, such as Turkey, wanted to make last-ditch pleas to Assad to stop the crackdown. "The Turks were publicly saying - not just privately saying - they wanted to give Assad one more chance."  

In recent weeks, figures from the right, such as Bush administration National Security Adviser Steven Hadley, and from the left, such as columnist and CNN host Fareed Zakaria, urged Obama to be more blunt in calling for an end to Assad's reign. Some analysts said the administration's slowness in turning against Assad reflects an initial reluctance among Obama aides to giving up hope on a rapprochement with Damascus.  

Senate Foreign Relations Committee Chairman John Kerry (D-Mass.) has visited Assad in Damascus four times since Obama took office, each time with the blessing of the White House. In a statement Thursday, Kerry called the need for Assad to go "obvious." Kerry referred only obliquely to his own diplomacy, saying that Assad "missed an historic opportunity for a new relationship with the west and economic transformation for Syria."  

Still, as recently as March, Clinton publicly referred to Assad "a different leader" than his father and a figure viewed by some in the U.S. Congress as "a reformer" -a comment Romney noted in his statement Thursday. Clinton also suggested at the time that Assad's violence was more limited than that inflicted by Libyan leader Muammar Qadhafi.

In the first two years of the Obama administration, officials also held out hope that Assad could help advance Middle East peace. A similar hope for Egyptian President Hosni Mubarak led to early expressions of support for him before Obama ultimately called in February for his ouster.

 U.S. officials said Thursday there is no chance now that Assad could help broker peace between Israelis and Palestinians.  

"We have a desire to see Arab-Israeli peace broadly speaking. We have no investment in individuals' particular involvement in that," another senior U.S. official said during the conference call. "President Assad's ability to be at all a figure in that [is] long gone. He has no legitimacy in his own country." 

Former State Department spokesman P.J. Crowley said the administration's reticence to demand Assad's ouster may also have reflected the reality that Obama's call for Qadhafi's exit has gone unheeded despite five months of NATO bombing. 

"Libya ... has been a much harder nut to crack than the White House initially anticipated. This has had a sobering effect in how to approach Syria," said Crowley, who has urged Obama for weeks to explicitly advocate an end to the Assad regime. "The administration arrived at a similar point with Assad as it did with Qadhafi (though there is no military option for Syria) but it obviously took longer to get there," he wrote in an email to POLITICO. 

In conjunction with Obama's announcement, the U.S. imposed new sanctions on Syria's energy sector - effectively banning American companies and individuals from doing business with Damascus. 

However, Clinton said in an interview last week that such a move would have little direct impact because most Syrian oil exports go to Europe, not the U.S. 

"We have very little stake in it," Clinton told CBS. "The real trick is to convince the Europeans and the Arabs and the Chinese and the Indians and others." 

European leaders indicated in their statements Thursday that they are considering sanctions that could have a serious economic bite in Damascus. 

Experts said administration officials know Assad is unlikely to heed Obama's call to leave, but that the Syrian leader is not the immediate audience for the new stance by the U.S. and its allies.

"It's directed both at the Syrian people and the elites around Assad who have not declared themselves," Malinowski said. "These dramas are always a contest of legitimacy and morale. ... Steps like this diminish the legitimacy and morale of the elites around the dictator and increase the legitimacy and morale of the opposition. You can say it's a symbolic move, but it's important because everyone in the country believes it's important."

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