To win, a presidential candidate must have a majority in the electoral college. Before adoption of the Twelfth Amendment (1804), in the event that no candidate had a majority, the House of Representatives (voting by states, with one vote for each state) was to choose the president from among the five candidates highest on the electoral list. Then, "after the choice of the President, the Person having the greatest Number of Votes of the Electors shall be the Vice President"; in case of a tie the Senate would choose the vice president. The Twelfth Amendment, however, resulting from the confused election of 1800 (see Jefferson, Thomas, and Burr, Aaron) provided that electors vote for president and vice president separately. It also reduced from five to three the number of candidates from among whom the House was to choose—in case no candidate had a majority (only two presidents, Jefferson and John Quincy Adams, have been elected by the House).
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.