The Obamas celebrate after the president's swearing in. (Getty)
Barack Obama has joined select political company, as by a quirk of history, he becomes only the second US president, after Franklin Roosevelt, to take the oath of office four times.
Roosevelt, who guided America through the Great Depression and World War II forged history the hard way, as he was the only US leader to be elected to four terms, serving in the White House from 1933 until his death in 1945.
After a new amendment to the Constitution was ratified in 1951 limiting presidents to two elected terms, Obama, and others elected to the White House, have no hope of emulating FDR's political longevity.
Obama will join the four oaths club thanks to a slip of the tongue.
Swearing in Obama at the West Front of the US Capitol in 2009, Chief Justice John Roberts mixed up the wording of the oath of office, which the newly minted president repeated.
Out of what officials said at the time was "an abundance of caution," Obama aides asked Roberts to head to the White House for a do-over the next day, this time with the words in the correct sequence.
On Monday, Obama matched the double oath taking of his first term, at his second inauguration, thanks to the calendar.
The 20th amendment to the US Constitution requires that presidential terms end at noon on January 20 @mdash; but according to tradition, when that date falls on a Sunday, the president takes the oath a second time in public the next day.
Roberts was on duty on Sunday to officially inaugurate Obama's second term at a private ceremony attended by the president's close family, and broadcast on television from the Blue Room of the White House.
This time there were no mistakes, as Obama took the oath, and the whole affair lasted less than a minute.
Just before noon on Monday, at the US Capitol, Obama will raise his right arm again, and place his left on Bibles once owned by ex-president Abraham Lincoln and civil rights hero Martin Luther King, to take his fourth oath.