WASHINGTON -- President Barack Obama decided the crisis in Syria, which he called "the worst chemical weapons attack of the 21st Century," required delay rather than action.
In asking Congress to approve the bombing of Syria, Obama reset the notion of presidential authority about war powers that had increasingly resided with the executive branch since the end of World War II.
It also represents one of the greatest gambles of his presidency in that he is seeking the approval from a Congress that, at least in the Republican-controlled House, has fought him at every turn on a wide range of subjects.
Obama's expression of conviction Saturday, and the moral outrage voiced by Secretary of State John Kerry just a day before, suggest they believe that they will win the debate once Congress is fully informed about the evidence.
The authority of the Senate and House in matters of war was debated intensely before the second conflict in Iraq.
Vice President Joe Biden, Kerry and Defense Secretary Chuck Hagel -- all senators at the time -- joined critics of the war who said President George W. Bush had overstepped his authority. Obama's criticism helped propel his election to the Senate and, eventually, the White House.
In an interview with the Boston Globe in 2007, Obama was asked in what circumstances, if any, a president would have constitutional authority to bomb Iran without seeking a use-of-force authorization from Congress.
"The president does not have power under the Constitution to unilaterally authorize a military attack in a situation that does not involve stopping an actual or imminent threat to the nation," Obama said.
Obama's decision marks a rare moment in the past half-century when a president unilaterally decided to give some power back.
"It's quite uncertain what a military strike is going to produce," said Robert Dallek, a presidential historian. "He really shouldn't go it alone. It's wise to bring Congress into it. It gets him much more of a broad consensus."
While "temporarily it would certainly undermine him" if Congress rejects his request, the risk of proceeding without backing is greater, he said. "If you run into difficulties, you're out on a limb. This way he's someone who's acted with political backing," Dallek said.
Lee Hamilton, a Democrat and former chairman of the House foreign affairs and intelligence committees, said the decision will help Obama with public opinion.
"You will have the support of the Congress, which shares the burden. It will help him internationally, which will see the country is united," Hamilton said.
Obama's words almost undercut the sense of indignation that he and Kerry expressed, and at the same time put new pressure on Republicans in Congress, who had been urging military force even as they had taken no responsibility for it with a vote.
Faced with few good options in the short run, Obama chose to pull back so that more time might change the calculus. Congress returns from recess on Sept. 9.
Now the administration has the task of persuading Republicans, especially those who represent a more isolationist and Libertarian strain on international affairs, to support a limited military strike that no one argues will end the civil war in Syria, and many have suggested may make it worse.