Every President since George Washington has had to fill the same constitutional requirements to become president. In order to become president, an individual must be a natural-born citizen of the United States, be at least 35 years of age, and have lived in the country for at least 14 years. In addition, the presidential oath of office must be administered before they take office.
United States Library of Congress, The Constitution of the United States of America: Analysis and Interpretation
Article II, Section 1, Clause 5 of the United States Constitution states:
No Person except a natural born Citizen, or a Citizen of the United States, at the time of the Adoption of this Constitution, shall be eligible to the Office of President; neither shall any Person be eligible to that Office who shall not have attained to the Age of thirty five Years, and been fourteen Years a Resident within the United States.
All Presidents from Martin Van Buren on were born in the United States subsequent to the Declaration of Independence. The principal issue with regard to the qualifications set out in this clause is whether a child born abroad to American parents is a "natural born citizen" in the sense of the clause. Such a child is a citizen as a consequence of statute.1 Whatever the term "natural born" means, it no doubt does not include a person who is "naturalized." Thus, the answer to the question might be seen to turn on the interpretation of the first sentence of the first section of the Fourteenth Amendment, providing that "[a]ll persons born or naturalized in the United States" are citizens.2 Significantly, however, Congress, in which a number of Framers sat, provided in the Naturalization Act of 1790 "that the children of citizens of the United States, that may be born beyond the sea, . . . shall be considered as natural born citizens."3 This phrasing followed the literal terms of British statutes, beginning in 1350, under which persons born abroad, whose parents were both British subjects, would enjoy the same rights of inheritance as those born in England; beginning with laws in 1709 and 1731, these statutes expressly provided that such persons were natural-born subjects of the crown.4 There is reason to believe, therefore, that the phrase includes persons who become citizens at birth by statute because of their status in being born abroad of American citizens.5 Whether the Supreme Court would decide the issue should it ever arise in a case or controversy—as well as how it might decide it—can only be speculated about.
Article II, Section 1, Clause 8 of the United States Constitution states:
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."
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, 1789,6 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 that 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.7 The idea next turned up in a message by President Lincoln justifying his suspension of the writ of habeas corpus without obtaining congressional authorization.8 And counsel to President Johnson during his impeachment trial adverted to the theory, but only in passing.9 Beyond these isolated instances, it does not appear that the oath adds anything to the President's powers.