Article II of the U.S. Constitution provides for the election of a President and Vice-President by electors chosen from each state. Originally, the Vice-President was the individual running for President who came in second: "In every Case, after the Choice of the President, the Person having the greatest Number of Votes of the Electors shall be the Vice President." The Twelfth Amendment reduced the likelihood that a President and Vice-President would be from different political parties. The Constitution only gives the Vice-President two jobs, one being to serve as President Pro Tem of the Senate in order to break a tie in that body. It is the other job that makes the Vice-President important--he is to serve as President in case of the death of the President while in office. For half a century, this provision was not invoked. That ended with the death of William Henry Harrison and the succession of John Tyler. In the next century, the Vice-President took over when a President was killed or died on four occasions, and a decade later, Vice-President Gerald Ford became President when Richard Nixon resigned. The mantra for the choice of Vice-President became "only a heartbeat away," yet presidential candidates continued to select a running mate based on political considerations rather than on the best person to take the Oval Office if required to do so.
Many see the selection of a running mate as one of the first tests of the leadership ability of the presidential nominee. As Donald Young writes: "The Presidential nominee should always be held responsible for the choice of his running mate" (Young 374). This has not always been true, however, as Jules Witcover notes when describing the process by which Richard Nixon was chosen as the running mate for Dwight Eisenhower in 1952. Nixon was chosen by Eisenhower's political advisers rather than by Eisenhower himself:
The choice of the man who might be the nation's next presi...