The Vice President is first in the line of succession to become President if the President is unable to serve. The document discusses how Vice Presidents are often chosen to balance the presidential ticket geographically, politically, or in terms of personality. It also explains the order of succession beyond the Vice President, which includes the Speaker of the House and President pro tempore of the Senate. The 25th Amendment further clarified the rules around presidential succession and established procedures for filling a vacancy in the Vice Presidency.