US President Barack Obama took the oath of office to begin his second term at a simple ceremony stripped of the hope and historic promise that greeted his inauguration four years ago.
Pageantry will come on Monday, when Obama retakes the oath in public at the US Capitol, but the brief swearing-in ritual at the White House epitomized the diminished resonance of a presidency unfolding in grinding economic times.
"I, Barack Hussein Obama, do solemnly swear..." Obama said, promising to "faithfully execute the office of President of the United States" and to "preserve, protect and defend the Constitution of the United States."
Obama, with a slight smile, took the oath with his right hand raised, and his left on a family Bible held by his wife Michelle, wearing a blue dress, to match the decor of the oval White House Blue Room hosting the ceremony.
Chief Justice John Roberts, who stumbled when swearing in Obama to open his first term in 2009, slowly read each line of the oath out loud, before the president repeated phrases first intoned by George Washington, 224 years ago.
Watched over by portraits of other former US leaders, including Thomas Jefferson and John Adams, Obama hugged his wife and children Malia, 14, and Sasha, 11, before quipping: "I did it" to his youngest daughter.
The cheeky Sasha shot back : "you didn't mess up!"
Michelle Obama later sent a personal tweet saying: "Barack just took the official oath at the @WhiteHouse & used my grandma's bible for the ceremony. I'm so proud of him. -- mo."
Later, Obama struck the kind of note of national unity that he will be expected to unfurl in his inaugural address on Monday, at a reception for supporters who helped him beat Republican Mitt Romney in November.
"What the inauguration reminds us of is the role we have as fellow citizens in promoting a common good even as we carry our individual responsibilities."
The president said the celebrations were also a reminder there was something larger than the individual and praised the "decency, the goodness, the resilience, neighborliness, the patriotism, the sense of duty, the sense of responsibility of the American people."
Obama, 51, will embark on a second term at a time of deep partisan division in Washington, and will face foreign crises testing his legacy, including Iran's nuclear program and resurgent Islamist militancy in North Africa.
Senior aide David Plouffe said the president would use his second inaugural address Monday before an expected 500,000 plus crowd -- much smaller than in 2009 -- to stress the national truths Americans share.
"He is going to talk about how our founding principles and values can still guide us in today's modern and changing world," Plouffe said on the ABC News show "This Week."
"He is going to say that our political system does not require us to resolve all of our differences or settle all of our disputes, but it is absolutely imperative that our leaders try and seek common ground."
Obama took the oath of office on Sunday to comply with the US Constitution, which dictates his first term ends at noon on January 20.
Tradition states that when that date falls on a Sunday, a private swearing-in is followed on Monday by the public festivities, including the second oath taking, the address, parade and glittering inaugural balls.
Vice President Joe Biden was sworn in before his boss at an early morning ceremony at his official residence, before the two laid a wreath at the Tomb of the Unknowns at Arlington National Cemetery.
Supreme Court Justice Sonia Sotomayor -- picked by Obama during his first term to be the first Hispanic judge to sit on the top court -- made her own slice of history by leading Biden as he took the oath.
Obama's second inauguration lacks the historical echoes of January 20, 2009, when he was sworn in as the first black American president.
Since then, a graying Obama has struggled to accelerate a weak economic recovery, failed to meet hugely elevated expectations for his presidency and waged a political war of attrition with Republicans.
He begins anew with several fierce budget battles looming in Congress, and his "Yes We Can" rhetoric soured by sarcasm over the blocking tactics of Republicans in the partisan brouhaha paralyzing government in Washington.
Abroad, the US confrontation with Iran is fast-headed to a critical point with the specter of military action becoming ever more real the longer diplomacy over Tehran's nuclear program remains stuck in neutral.
And terror strikes that killed Americans in Benghazi and Algeria call into question Obama's election year sound bite that "Al-Qaeda is on the run," despite the killing of Osama bin Laden in Pakistan in 2011.
Muscle-flexing by China and rising tensions in contested waters with its neighbors, as well as North Korea's nuclear belligerence, will meanwhile test the president's signature pivot of US diplomacy to Asia.