<P> In the United States, "running mate" refers not only to a candidate for vice president (federal), but also to a candidate for lieutenant governors of those states where the governor and lieutenant governor are jointly elected . Historically, American running mates were chosen by political parties in consultation with the principal candidate (i.e., the person running for president or governor). In the late 1960s, it became the practice of the principal candidate in presidential elections to announce his or her preferred choice of running mate at his or her political party's national convention . The current practice is for the presumptive nominee of a political party to announce his or her choice for running mate before the national convention which, because of the extensive primary election and caucus system, is becoming increasingly irrelevant . </P> <P> The practice of running candidates for president and vice president together evolved in the nineteenth century . Originally, electors cast two ballots for president and whoever took second place in the tabulation became vice president . Starting in 1804, the president and vice president were elected on separate ballots as specified in the Twelfth Amendment to the United States Constitution which was adopted in that year . As more and more states subsequently began to choose their electors by popular election instead of appointment (South Carolina being the last state to change, in 1860), candidates began to realize they could run together as a team for president and vice president instead of running completely separately for each office . </P> <P> The practice of a presidential candidate having a running mate was solidified during the American Civil War . In 1864, in the interest of fostering national unity, Abraham Lincoln from the Republican Party (popular in the North) and Andrew Johnson of the Democratic Party (popular in the South), were co-endorsed and run together for President and Vice-President as candidates of the National Union Party . Notwithstanding this party disbanded after the war ended, with the result that Republican Lincoln was succeeded by Democrat Johnson; the states began to place candidates for President and Vice-President together on the same ballot ticket - thus making it impossible to vote for a presidential candidate from one party and a vice-presidential candidate from another party, as had previously been possible . </P> <P> Presidential candidates from smaller states sometimes choose a vice presidential running mate from a state with a large number of electoral votes - as when Walter Mondale of Minnesota (10 votes) selected Geraldine Ferraro of New York (then 36 votes). It is preferred, but not legally required, that the running mate be from a different state from the presidential nominee, because each elector can vote for no more than one candidate from his or her own state . Running mates can also be chosen from swing states in order to boost a candidate's chance of winning in the state . </P>

When did presidential candidates start choosing running mates