Joseph Robinette Biden Jr. was sworn in as president on Wednesday at 11:48 a.m. local time in Washington DC, on the steps of the convention hall.

Both the sworn President of the U.S. Supreme Court, John Roberts, and Senator Amy Klobuchar, who led the ceremony, congratulated Biden as “Mr. President”.

However, according to experts interviewed by the Washington Post (WP), Biden was not yet president even though he had sworn in.

His presidency did not begin until 12 minutes later, at 12 noon.

Experts refer to Appendix 20 to the Constitution, which says the terms of office of the president and vice president will end on January 20 at noon.

"The oath of office must be sworn, but it doesn't make a person president," Jonathan Turley, a law professor at George Washington University, told WP.

Another expert, Robert Chesney, a professor of law at the University of Texas, told the Post that it was logical for the president to swear an oath of office before the start of his term.

- It would be special if there was a rule that stipulated that there should be some time after which the oath of office could be sworn.

Then there would be a situation where there would be a momentary phase where the country would have no president at all, Chesney recalled.

It is not known why Biden was sworn in early.