because it is a tradition and custom
Oath of Office
All US presidents take the oath of office, starting with the first president, George Washington.
James MonroeThe first president to take the oath was George Washington.
President Obama swore the oath of office on Abraham Lincoln's Bible.
Yes- the President must take the oath of office as required by the US Constitution.
Joe Biden would serve as the President and therefore take the oath of office in the case the Obama did not.
April
First he has to be legally elected as President or else become president by succession. Second he must be "sworn in" by taking the oath of office before a person who is legally qualified to administer oaths.
I think the president becomes official at NOON the day of inauguration, whether he takes the oath or not.
Lyndon Johnson
at noon
In Philadelphia - in 1789.