Every president of the United States has recited the oath of office as the official start of their presidency.
The oath is found in Article II of the Constitution. It contains 35 words and goes as follows:
"I do solemnly swear (or affirm) that I will faithfully execute the Office of President of the United States, and will to the best of my ability, preserve, protect and defend the Constitution of the United States."
The vice president-elect takes a slightly different, longer oath, which is also utilized for members of Congress and some other federal employees:
"I do solemnly swear (or affirm) that I will support and defend the Constitution of the United States against all enemies, foreign and domestic; that I will bear true faith and allegiance to the same; that I take this obligation freely, without any mental reservation or purpose of evasion; and that I will well and faithfully discharge the duties of the office on which I am about to enter: So help me God."
Note that POTUS does NOT say anything about the ENEMIES of our country.
However, the VICE president does. So unless Joe has disavowed his previous OATH; it is STILL binding.