WASHINGTON - Barack Obama took the 35-word oath of office Tuesday to become the United States' 44th president -- even if he may have been led to utter the historic words in the wrong order.
Obama was sworn in by Supreme Court Chief Justice John Roberts, resting his left hand on Abraham Lincoln's Bible and raising his right hand to deliver the words that formally made him the successor to former president George W. Bush.
But things didn't go exactly as planned for the swearing-in of the country's first African-American commander-in-chief.
Under the gaze of more than two million crowded onto Washington's National Mall and millions more around the world, Obama said: "I, Barack Hussein Obama, do solemnly swear that I will execute the office of president of the United States faithfully, and will to the best of my ability, preserve, protect, and defend the constitution of the United States.
"So help me God."
As specified in the US Constitution, the word "faithfully" precedes the phrase "execute the office," but the chief justice, in his first presidential inauguration, read that part of the oath incorrectly.
Obama paused, apparently realizing something was wrong, and after an awkward moment Roberts repeated himself, but the chief justice stumbled again. Obama eventually recited the line as Roberts originally said it.
Huge crowds watching the historic proceedings one mile (kilometer) down the National Mall on a jumbo TV screen groaned loudly after Roberts' gaffe.
"Oh no, no no no!" one woman screamed above the murmuring crowd.
The stumble marks the first of what is expected to be several interactions between the two men whose politics differ broadly.
Roberts, 53, was nominated to the high court by Obama's predecessor George W. Bush in 2005, as the youngest chief justice in more than 200 years.
Roberts served in Republican administrations before becoming an appeals court judge and eventually chief justice.
Obama was among 22 Democrats in the US Senate to vote against Roberts in his Supreme Court confirmation hearing.
In Obama's first luncheon as president, the affable Roberts appeared to apologize, prompting laughter and a handshake from Obama.
The new president could fill vacancies in the Supreme Court -- some aging liberal justices are known to want to retire -- as a means of countering Roberts's influence.
Jeffrey Rosen, a US constitutional law expert and professor at George Washington University in Washington, said stumbling over the oath has "no impact. News flash: He's president."
Rosen pointed to the 20th amendment of the US Consitution, which provides that the president and vice president's term begins at noon on January 20th.
"Lots of people have flubbed the oath, perhaps most memorably Chief Justice (William Howard) Taft, who sort of riffed and then made up his own" upon swearing in then-president Herbert Hoover, said Rosen.
Where the oath calls for the president to pledge to "preserve, protect, and defend" the constitution, Taft said "preserve, maintain and defend" -- injecting an entirely new word, while Roberts merely got the order wrong.