Barack Obama was ready to order a military strike against Syria, with or without Congress' blessing. But he suddenly changed his mind.
Senior administration officials describing Mr Obama's about-face offered a portrait of a president who began to wrestle with his own decision - at first internally, then confiding his views to his chief of staff, and finally summoning his aides for an evening session in the Oval Office to say he had a change of heart.
The ensuing flurry of activity culminated yesterday in the White House Rose Garden when Mr Obama stood under a sweltering sun, his vice president at his side, and told the American public the US should launch a military strike to punish Syrian president Bashar Assad for a chemical weapons attack the US says killed more than 1,400 people last week.
But first, he said, he would ask permission from Congress.
Here, according to officials, who spoke anonymously, are the key events that led to Mr Obama's decision.
:: By the time Mr Obama's National Security Council met a week ago, a few days after the attack, it was clear the intelligence the US had gathered corroborated the notion that a chemical attack had resulted in dramatic mass casualties.
As the meeting opened, Mr Obama told his advisers the attack outside Damascus was precisely the type of scenario he had been concerned about last year, when he said Assad's large-scale use of chemical weapons would cross a red line for the US and necessitate a response. Mr Obama had not made a final decision, officials said, but told aides his strong inclination was the US must act.
By the end of the meeting, aides were no longer discussing whether to respond, but how and when.
:: Over the course of the next week, Mr Obama's aides began making their case publicly, asking allies to support a military action and talking with politicians, who were away from Washington in the final throes of their August congressional recess.
Secretary of state John Kerry cut short his own holiday and was dispatched to say the US had clear evidence of an attack, in two impassioned State Department speeches. And defence secretary Chuck Hagel, travelling in Asia, said the US had moved military assets into place and "we are ready to go". The US Navy beefed up its presence in the Persian Gulf region, increasing the number of aircraft carriers from one to two.
:: Away from Washington, the US was running into obstacles in its search for a global coalition to bolster its case that a response was needed to protect a international norm against chemical weapons use.
Its own inspectors on the ground in Syria, the United Nations Security Council failed to reach agreement on Wednesday on authorising the use of force, with Russia objecting to international intervention. Meanwhile, Mr Obama declared publicly and unequivocally that the US had concluded Assad's government carried out the attack.
Thursday brought another stinging setback when a vote in Britain's parliament to endorse military action failed, all but guaranteeing the UK would not play a direct role. But France's leader said he and Mr Obama were in agreement and that France could go ahead with a strike.
:: In Washington, politicians from both parties were insisting Mr Obama consult more closely with congress before giving an order to begin hostilities. Dozens, most of them Republican, signed a letter saying he should not take military action without congressional approval, although administration officials insisted no congressional leaders or committee chairman made that request personally to the White House.
Mr Obama's national security team was in agreement that while consulting with congress was critical, there was no need for formal approval, officials said. Seeking a vote in congress to authorize a strike was not even an option on the table.
:: All that changed on Friday night, when Mr Obama left the West Wing with his chief of staff, Denis McDonough. Under cloudy skies and temperatures nearing 90 degrees Fahrenheit (32 degrees Celsius), the two walked on the White House grounds for the better part of an hou, and Mr Obama confided in his adviser that he had changed his mind and laid out an idea to ask congress to approve a strike.
By 7pm, top aides including deputy national security advisers Ben Rhodes and Tony Blinken had been summoned to the Oval Office, where Mr Obama shared the new plan. It was the right thing to do, the president said, and would make the US stronger.
Aides went to work immediately, with some drafting an authorisation that congress could take up and others hashing out the timeline.
:: But the next morning, there was opposition from some on the president's team. The National Security Council convened to firm up the plan, with vice president Joe Biden, defence secretary Chuck Hagel, director of national intelligence James Clapper, CIA director John Brennan, national security adviser Susan Rice and others attending.
When Mr Obama said he wanted to ask Congress for a vote, some of his advisers dissented. Officials would not say who argued against his proposal.
After a two-hour debate, Mr Obama's team agreed to support the president's decision, officials said. Mr Obama went upstairs and called the Republican and Democratic leaders of the House and Senate to inform them of his about-face. He also notified French president Francois Hollande.
By mid-afternoon, Mr Obama emerged in a steamy White House Rose Garden, surprising politicians, reporters and the public with news of his plan.
"I'm ready to act in the face of this outrage," Mr Obama said. "Today I'm asking congress to send a message to the world that we are ready to move forward together as one nation."
He and Mr Biden then left the White House by motorcade to play a round of golf.