re: #19 Semper Fi

I would like to think the sitting prez must vacate the White House in event he/she loses the election. Is that the law or has it only been gentleman’s agreement? I would like to have a warm and confident feeling backed by law because the Trumper is not a gentleman.
Does anyone know if the loser is compelled by law to vacate the WH?

The law is this: On Jan 21, 2021, the new president will be sworn in. At that point, Trump is no longer president, and if he stays, he is illegally occupying the White House.