Under the Constitution, the vice president serves as the president of the Senate (voting only to break ties) and succeeds the president in the event of death, resignation, or the inability of the president to discharge duties. The process of presidential succession was changed through the Twenty-fifth Amendment, which was a response to the transition following the assassination of President John F. Kennedy in 1963. The orderly transition of power in the executive branch is one of the hallmarks of U.S. constitutional government.
The selection of the vice president
Although the vice president is only "a heartbeat away from the presidency," politics influences this individual's selection more than any qualifications to hold the highest office. President Kennedy chose Lyndon Johnson as his running mate primarily because Johnson was a Southerner who could help carry the key state of Texas; that Johnson was the powerful majority leader of the Senate was less important. Walter Mondale's background in the Senate, on the other hand, made him a logical vice president for Jimmy Carter, who was the governor of Georgia and running as a Washington outsider. In the case of Dick Cheney, George W. Bush's vice president, experience was likely key; while the president had been a two-term governor of Texas, Cheney served in Congress, as White House chief of staff, and secretary of defense.
The role of the vice president
Because of a limited constitutionally defined function, the role that a vice president plays is determined by the president. While Harry Truman was vice president, he was kept in the dark about many key issues. He did not learn about the atomic bomb, for example, until after he became president following the death of Franklin Roosevelt. Since 1960, however, the responsibilities of the vice president have expanded. Lyndon Johnson led the nation's space program under Kennedy. Al Gore was heavily involved in the Clinton administration's policies, especially in areas such as foreign policy, the environment, and streamlining government. Dick Cheney played a key role in developing the Bush administration's energy policy as well as military strategy after the events of September 11, 2001.
The process of presidential succession
Following the assassination of John F. Kennedy, Lyndon Johnson served for more than a year without a vice president. This situation was addressed by the Twenty-fifth Amendment (1967). When a vacancy in the vice presidency exists, the president nominates a person for that office; the candidate must be confirmed by a majority of both houses of Congress. This process was followed twice in the 1970s, when Gerald Ford became vice president after Spiro Agnew resigned and when Ford appointed Nelson Rockefeller as his vice president after President Nixon resigned. The amendment also provides for the temporary transfer of power to the vice president if the president is incapacitated. In the event that the offices of both president and vice president are vacant simultaneously, the order of succession is the Speaker of the House of Representatives, the president pro tempore of the Senate, followed by the heads of the cabinet departments in the order in which they were created, beginning with the secretary of state.