What do the President of the United States and members of his cabinet take an oath to? Is it the Constitution or something else?

Each time the President takes the following oath (in accordance with Article II, Section 1 of the U.S. Constitution):

"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."

Article 2, Section 1 of the U.S. Constitution provides the following oath of office for the President: "I do solemnly swear that I will faithfully execute the Office of President of the United States, and will to the best of my Ability, observe, preserve, and defend the Constitution of the United States."

The Vice President-elect and other federal officers take the oath of office by the following oath: "I do solemnly swear that I am determined to preserve and defend the Constitution of the United States against all enemies, foreign and domestic. I will be faithful and true to the Constitution. I undertake this duty voluntarily, without reservation or imputation. I shall be faithful and diligent, and shall devote myself to the execution of the duties of the office which I am about to assume. May God help me."