President Biden will take the oath of office today.
Many posts have discussed oaths of office.
From the Legal Information Institute:
What is the time relationship between a President’s assumption of office and his taking the oath? Apparently, the former comes first, this answer appearing to be the assumption of the language of the clause. The Second Congress assumed that President Washington took office on March 4, 1789,128 although he did not take the oath until the following April 30.
That the oath the President is required to take might be considered to add anything to the powers of the President, because of his obligation to “preserve, protect and defend the Constitution,” might appear to be rather a fanciful idea. But in President Jackson’s message announcing his veto of the act renewing the Bank of the United States there is language which suggests that the President has the right to refuse to enforce both statutes and judicial decisions based on his own independent decision that they were unwarranted by the Constitution.129 The idea next turned up in a message by President Lincoln justifying his suspension of the writ of habeas corpus without obtaining congressional authorization.130 And counsel to President Johnson during his impeachment trial adverted to the theory, but only in passing.131 Beyond these isolated instances, it does not appear to be seriously contended that the oath adds anything to the President’s powers.