* Advisers surprised by Obama's call to turn to Congress
* British parliament vote affected president's thinking
* Risks, and criticism about his leadership
At the end of the day on Friday, after laying out a strong public case for U.S. military action in Syria, President Barack Obama took a 45-minute walk around the South Lawn of the White House with his chief of staff, Denis McDonough.
They discussed Obama's options for using force.
Despite saying for days that he had not yet made a decision, the president had been leaning toward military intervention since initial reports from his advisers that Syrian President Bashar al-Assad had used chemical weapons to kill innocent civilians near Damascus, senior officials said on Saturday.
But after a week of laying the groundwork for a targeted attack, Obama had begun to waver about immediate action. Britain, Washington's closest ally, had opted out of an international coalition after its parliament said "no," a decision that weighed on the president.
Republican leaders in Congress, who control the fate of large parts of Obama's domestic policy agenda, had complained loudly about a lack of consultation from the White House ahead of a potential new war.
And polls showed war-weary Americans remained opposed to U.S. involvement in Syria, despite the devastating photos of dead children and their gassed parents.
So the president decided to wait. Rather than ordering a military strike, he would announce his decision that force was necessary while seeking congressional approval to authorize it.
"After careful deliberation, I have decided that the United States should take military action against Syrian regime targets," he said on Saturday in the White House Rose Garden, Vice President Joe Biden standing at his side.
"I'm also mindful that I'm the president of the world's oldest constitutional democracy ... and that's why I've made a second decision: I will seek authorization for the use of force from the American people's representatives in Congress."
The decision surprised his own advisers, who had not proposed voluntarily seeking lawmaker approval and had concluded Obama had the legal authority to take action on his own. But Obama felt it would be more consistent with his desire, stated earlier this year, to take America off of a "perpetual wartime footing" by getting the backing of Congress and the citizens it represents.
After his walk with McDonough, the president called National Security Adviser Susan Rice, her deputy Tony Blinken, senior adviser Dan Pfeiffer, and others into the Oval Office to announce his approach.
They had a vigorous debate that lasted two hours, senior administration officials said. The biggest risk to Obama's new plan: Congress, like the British parliament, would vote no. That would cast serious doubts on Obama's ability to lead in the Middle East where he is already under fire for what critics call a muddled response to the Egyptian military coup.
The benefits outweighed that risk for Obama, who believed lawmakers would be compelled to vote for a measure that would protect U.S. allies Israel and Jordan.
Adding further weight to the idea of a delay, his military advisers said that waiting on a strike would not make it less effective. Assad, the administration believed, was unlikely to conduct another chemical weapons attack while a U.S. threat loomed. A 'yes' vote would give Obama more legitimacy to attack Syrian forces.
And Congress now would share in the responsibility of a decision that could prove unpopular for Obama either way.
RISKS AND CRITICS
Still, it was a risk. Analysts say Assad could use the time to move weapons to more populated areas of Syria. And a difficult debate in Congress could worsen already bad relations between the White House and Capitol Hill.
"The decision to get Congress on board when he hasn't had a huge amount of success working with Congress strikes me as a gamble," said Jon Alterman, director of the Middle East Program at the Center for Strategic and International Studies.
A failed vote, he said, "could shadow the rest of the administration."
Colin Kahl, a Georgetown University professor and former Defense official, said the passage in the Democrat-controlled Senate was assured, while the Republican-controlled House of Representatives was likely as well.
"There are some skeptics both on the left and the right in the Congress, but I think the administration has a pretty strong case that we need to do this," he said.
"If they start to think through some of the credibility implications of not authorizing this, especially as it relates to Iran, then it will pass in the House."
After making his statement at the White House, Obama and Biden went out for a round of golf.
Lawmakers from both political parties who support action said the president had failed to react as quickly as necessary.
"I support the president's decision. But as far as I'm concerned, we should strike in Syria today," said Bill Nelson, a Democratic senator from Florida who is a senior member of the Senate Armed Services Committee.
"Leadership is about reacting to a crisis, and quickly making the hard and tough decisions," said Senator Saxby Chambliss of Georgia, the top Republican on the Senate intelligence committee. He said Obama should have demanded that lawmakers, who are on recess until Sept. 9, return to Washington immediately.