His longstanding vision for progressive change faced sharp and unexpected repudiation Tuesday night from voters still fuming at their perceived diminished prospects. By Obama's own admission, the major pieces of his presidential legacy are now subject to a gutting by a successor he resents deeply.
But the President insisted to his supporters and Democrats Wednesday this is not the end.
"The sun is up, and I know everybody had a long night. I did as well," Obama said in the White House Rose Garden.
Obama will likely leave office with an approval rating of over 50%, and it's a truism of American politics that ex-presidents get more popular after they leave the White House.
Nothing, however, can paper over the fact that the first African-American president will stand on the inaugural platform next to Donald Trump, who stoked divisions and preyed on people's racist fears, including through lies and insinuations about Obama himself.
Obama's efforts on Hillary Clinton's behalf over the past month, unprecedented for a modern sitting president, reflected not only a desire to elect his former secretary of state. It was a chance to sell, again, his vision of a hopeful America and the progress inherent in a nation ready to elect its first African-American president.
The US electorate affirmed that vision in 2008, and gave Obama more time to fulfill it in 2012. But voters now leave Obama with little hope of salvaging a presidential legacy that depended heavily on his successor.
Trump and Obama will meet Thursday, and the President said the White House will cooperate with the incoming administration, citing the example President George W. Bush set in 2008.
"Everybody is sad when their side loses an election, but the day after we have to remember that we're actually all on one team," Obama said. "This is an intramural scrimmage. We're not Democrats first. We're not Republicans first. We are Americans first. We're patriots first. We all want what's best for this country. That's what i heard in Mr. Trump's remarks last night. That's what I heard when I spoke to him directly. And i was heartened by that. That's what the country needs. A sense of unity, a sense of inclusion, a respect for our institutions, our way of life, rule of law, and a respect for each other. I hope that he maintains that spirit throughout this transition, and I certainly hope that's how his presidency has a chance to begin."
But the sting of Trump's victory will last well beyond the transition period as the framework of Obama's presidential legacy comes under siege by Republicans who fought him tooth and nail for eight years and who, in January, will control the White House and both chambers of Congress.
During rally after rally on Clinton's behalf, Obama cautioned voters that electing Trump would mean watching his accomplishments on jobs, health care, foreign policy, climate change and equality go "down the drain."
He warned his coalition of African-Americans and young people that he would "consider it a personal insult -- an insult to my legacy" if they didn't propel Clinton to the type of electoral victory they helped him achieve. Those voters did not turn out in the same levels they did for Obama, despite his aggressive overtures.
During every battleground rally or radio phone-in, he declared Trump "uniquely unqualified" to hold his office, warning against allowing the brash billionaire near the nuclear codes. He spent the last 18 months reassuring his foreign counterparts that Trump's proclamations about America don't reflect the country's real values.
Like all Democrats, Obama faces a reckoning about the true makeup of the American electorate, and his party's prospects going forward. But he also awakens Wednesday with the bitter responsibly of handing the US government to the man whose actions he openly fears.
"This is somebody who would do damage to our democracy," Obama said of Trump in Florida last week, adding Trump made him "fear for the Republic."
Readying assault on Obama priorities
Trump has promised to scrap Obama's signature health care law, which has become increasingly fragile as costs spike and insurers withdraw from exchanges. The fixes that Obama insists will reinforce the Affordable Care Act now appear to have little chance of moving forward.
Trump's transition team has been developing plans to reverse the patchwork of executive actions that Obama devised to skirt a Republican Congress on immigration and climate change. That includes Obama's unilateral moves easing deportation enforcement and his regulations on power plants.
Even before Obama leaves office, those actions remain mired in legal challenges and haven't yet taken effect. Proponents of the moves had claimed if they eventually did take hold, their positive impact on society would make it difficult for future presidents to reverse them. Having never taken full effect, there's little expectation now those actions will ever be realized.
Trump has committed to withdrawing the US from trade agreements, including the pending Trans Pacific Partnership that Obama has championed. So, too, has Trump said he would remove the US from the agreement with Iran to curb its nuclear ambitions and from a global climate accord signed in Paris last year.
The fate of the Supreme Court, with a GOP Senate now under no pressure to take up Obama's nomination of Merrick Garland, is likely sealed. Trump has named several conservatives
as potential justices; it's likely he'll have multiple seats to fill as the court's older members approach retirement.
Tone of final months
In the coming weeks, administration officials are expected to work on cementing what elements of Obama's unfinished agenda they can, either through new executive orders or action in the lame duck Congress.
Obama himself is expected to deliver a major address on democracy next week in Greece -- the ancient birthplace of that type of government -- and to meet for a final time with close US allies. Those meetings are now expected to center on shoring up shared priorities as trans-Atlantic alliances face an uncertain future.
But even as Obama works in his final weeks to salvage what he can of his agenda, there's little doubt that his message of hopefulness has suffered a deep setback.
The tone of the just-concluded presidential contest is perhaps the best reflection of his inability to improve the tenor of American political life. When he announced his presidential run in 2007, Obama decried the "the smallness of our politics" and vowed to reform Washington.
Eight years later, the race to succeed devolved into one of the darkest national election races in memory, a bitter and ugly fight between two deeply unpopular candidates.
"It's one of the few regrets of my presidency that the rancor and suspicion between the parties has gotten worse instead of better," Obama said in his final State of the Union address earlier this year.