Someone who has been President can run for Vice President if he/she has not served two terms as President. Because the President is limited to two terms, and the Vice President must be eligible to...
Thirty-five.
From Article II, Section 1: "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...
A Democrat could run for the Democratic nomination against an incumbent Democratic President. This happened in 1980 , for example, when Ted Kennedy ran against President Carter. Of course only one...