The Constitution specifies the following:
Before he enter on the Execution of his Office, he shall take the following Oath or Affirmation:—"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."
However, most scholars agree that Zachary Taylor's term began on March 4, 1849, despite not taking the oath until the following day.
What does taking the presidential oath actually change?