He was the peace candidate who became a war president, a Nobel Peace Prize laureate who has regularly ordered executions by drone.
Just three months ago, President Barack Obama called for an end to America's "perpetual war-time footing." Now he has ordered the U.S. military into position for an aerial strike in Syria - with neither hopes it will end that country's cataclysmic civil war, nor the backing of the broad global coalition he wanted.
If any more proof were needed that history can defy the most firmly held convictions, the Obama presidency is it.
Since the war in Syria began, the president has repeatedly denounced the killing of innocent civilians - more than 100,000 people have already died in the conflict - while declaring his determination to avoid getting the United States sucked in.
Obama's announcement a year ago that Syria President Bashar al-Assad's use of chemical weapons would constitute a "red line" was followed by evidence this spring that that line had been crossed. Yet there was no military response. White House officials said Washington would respond by providing lethal aid to the opposition Syrian Military Council; but it is unclear if any has arrived.
After more than two years of tough talk and military restraint, some current and former aides believe the cautious president has now left himself no choice but to act forcefully against Assad.
"The 800-pound gorilla in the room is the question of maintaining American credibility," a former senior administration official said as a U.S. military response loomed after a massive Aug. 21 poison gas attack that U.S. intelligence blamed on Assad and his military.
With neither a United Nations mandate nor the expected British military support, the Obama administration faces the prospect of undertaking military action against Syria with even less international and domestic support than George W. Bush had for the Iraq war, which Obama voted against.
There is a crucial difference: Obama is contemplating a two- to three-day cruise missile strike, not a ground invasion. That, critics say, is the conundrum: What can be achieved by such a limited application of force?
Underlying the humanitarian grounds and national security concerns that Obama and Secretary of State John Kerry laid out was a kind of resignation, an acceptance that - like it or not - there are still times the United States must serve as global policeman.
"Ultimately we don't want the world to be paralyzed," Obama said to reporters at a meeting with Baltic leaders at the White House on Friday afternoon. "And, frankly, you know, part of the challenge that we end up with here is that a lot of people think something should be done, but nobody wants to do it."
For a man who entered the White House in 2009 promising a swift withdrawal from Iraq and a new era of multilateralism after eight years of the Bush administration's so-called "cowboy diplomacy", the predicament could hardly be more poignant.
Obama has hardly been or presented himself as a pacifist. While running for office he declared his opposition only to "dumb wars," not all of them. And he continued the fight his predecessor had begun against al-Qaida, only with different means.
Once in the White House, he quickly turned the military's focus from Iraq to Afghanistan, which his aides had touted as the "good war" in the fight against Islamic militants.
In 2010, he surged 33,000 additional troops to Afghanistan, but gave his generals fewer troops and less time than they wanted. The last of the surge troops returned home a year ago, and Obama plans to have U.S. combat forces out by late 2014.
Obama sharply expanded the Bush administration's program of drone strikes, and the presidential "kill list" proved effective in taking out al-Qaida militants in Afghanistan, Pakistan and Yemen without putting U.S. forces in harm's way.
In May, against a background of civilian casualties, growing anti-American sentiment and escalating criticism of the drone strikes at home, Obama narrowed the targeted-killing campaign, saying it was time to step back from a "boundless global war on terror." But the strikes continued.
Obama also deployed the military in NATO's bombing campaign against Libya's Moammar Gadhafi in 2011, citing the need to avert a mass slaughter resulting from government assaults on rebel-held territory. His approach, predicated on Americans' war-weariness, was described by one White House adviser as "leading from behind," with U.S. forces supporting a British- and French-led air assault. But the mission succeeded.
Then "Arab Spring" revolutions spread to Syria. On Aug 18, 2011, as Syrian government repression of protesters escalated dramatically, Obama called on Assad to give up power, a move he coordinated with leaders of Britain, France, Germany and Turkey.
Syria's civil war, the one he seemed most determined to avoid, has become his thorniest foreign-policy challenge, leading to what critics describe as a record of half-steps and miscalculations.
Misjudging Assad's staying power, the administration did little to hasten Assad's departure. As the war escalated in 2012, the President resisted calls to arm the rebels, fearing that weapons might fall into the hands of radical factions.
Some say Obama strayed from his talking points a year ago when he said Assad's use of chemical weapons would be a "red line." Others say the statement was intentional.
Whatever the source of the rhetoric, the Administration put its full weight behind the assertion Friday that the intelligence is clear: Chemical weapons were used, and the Assad regime used them. Among the White House's calculations now is that, if the United States does not act, others - including Iran, with its nuclear program - will see the West's warnings as empty threats.
Obama's friends say he is moved by a sense of moral imperative as well. "Knowing him," said former Obama press secretary Robert Gibbs, "the effects of what that attack did to innocent men, women and children .... are jarring to the point of requiring action."
Some senior Republicans say the measured attack under consideration - a stand-off attack by missiles from outside Syrian airspace - will not be enough.
"It does not appear that the response to this historic atrocity being contemplated by the Obama administration will be equal to the gravity of the crime itself," Republican U.S. Senators John McCain and Lindsey Graham said in a joint statement. "The purpose of military action in Syria should not be to help the president save face."
At the same time, the strikes on Syria may give Obama political problems during his last three years in office with the anti-war camp that helped elect him in 2008 and re-elect him last November.
"The response I'm getting in Connecticut is overwhelmingly negative when it comes to military intervention in Syria, and I think those people deserve to have their voice heard," said Democratic U.S. Senator Chris Murphy. Like Obama, Murphy was elected, in 2006, as an anti-war candidate.
(Additional reporting by Steve Holland, Arshad Mohammed and Patricia Zengerle; Editing by Warren Strobel and Gunna Dickson)© (c) Copyright Thomson Reuters 2013.