The Twelfth Amendment sets out the procedures for the election of the president and vice president. Electors cast one vote for each office in their respective states, and the candidate having the majority of votes cast for a particular office is elected. If no person has a majority for president, the House of Representatives votes from among the top three candidates, with each state delegation casting one vote. In the case of a failure of any vice presidential candidate to gain a majority of electoral votes, the Senate chooses between the top two candidates. The procedure for choosing the president and vice president is set out in Article II, Section 1, Clause 2 through Clause 6, of the Constitution. This amendment replaces the third clause of that section, which had called for only a single set of votes for president and vice president, so that the vice presidency would go to the presidential runner-up. In the unamended Constitution, the choice in the case of a non-majority in the Electoral College fell to the House of Representatives, as it does under the amendment, and the runner-up there would be chosen as vice president.

The Twelfth Amendment, the last to be proposed by the founding generation, was proposed for ratification in December 1803 and was ratified in 1804, in time for the presidential election that year. The previous system had yielded, in 1796, Federalist John Adams’s election as president, while his bitter rival and sometimes close friend, Republican Thomas Jefferson, was elected vice president. In the election of 1800, Republican electors, though they clearly preferred Jefferson, sought to guarantee that Republicans won both offices, and cast seventy-three electoral votes for both Thomas Jefferson and Aaron Burr. This threw the election into the House of Representatives, where it was only resolved (in Jefferson’s favor) on the thirty-sixth ballot. The hardening of party lines, concomitant voting by party slates (which the Framers had not contemplated), and some dissatisfaction with the way in which electors were chosen in the states led to proposals for change, including a proposal that electors be chosen in separate electoral districts in each state. However, the only change successfully accomplished was that of separate voting for president and vice president.

Although it remains theoretically possible for the vice president to be someone other than the person designated by the president and his party, the Adams-Jefferson scenario, in which the top two presidential candidates must perforce form a partnership, is now much more unlikely. In fact, Jefferson refused to assist Adams in his administration and actively sought to frustrate the president’s policies. In Ray v. Blair (1952), the Supreme Court held that a state could constitutionally impose a pledge from elector candidates to vote for their party’s nominees in the Electoral College. However, electors have defected from time to time. In 1988, one elector voted for Lloyd Bentsen as president rather than the Democratic nominee, Michael Dukakis. In 2000, Al Gore electors from the District of Columbia did not cast a vote, in protest of the fact that the district is not treated as a state under the Constitution. The extent to which the electors are bound to vote for the candidate of the party under whose designation they were elected as electors and whether all electors from a state are bound to vote as a bloc remain matters for each state to determine “in such manner as the legislature thereof shall direct.” Article II, Section 1, Clause 2. At the present time, electors in all but two states (Maine and Nebraska) do vote as a bloc, effectively ensuring a two-party system, though other states are considering choosing electors by congressional district.

Most presidential elections have not generated Twelfth Amendment controversy. However, the provisions of the amendment have surfaced from time to time, most commonly when a third-party candidate threatens to take a substantial percentage of the vote. In 1824, the failure of either Andrew Jackson or John Quincy Adams to garner a majority of electoral votes threw the election into the House of Representatives, where Adams won the presidency despite having fewer electoral votes than Jackson. In 1876, similar circumstances were resolved differently, when neither Rutherford B. Hayes nor Samuel J. Tilden received a majority of electoral votes because of disputed votes in three Southern states. In that instance, Hayes won the presidency when a congressional commission awarded him all disputed electoral votes (and thus a one-vote majority).

The Twelfth Amendment also effected a less significant change by providing that if the House does not complete its selection by Inauguration Day, the vice president shall act as president. The Constitution had already set out in Article II, Section 1, Clause 6, as was repeated in the amendment, that the powers and duties of the presidency would devolve on the vice president in case of the president’s death or disability. The procedure to be followed in the event of a failure to designate a president and related matters are now regulated by the Twentieth and Twenty-fifth Amendments.

The procedures for the selection of the president and vice president set out in this amendment have been more closely specified by 3 U.S.C. §§ 1–21. These provisions address the certification, delivery, and counting of the electoral ballots and the procedure to be followed if that count does not result in clear winners. Those procedures, as when there is controversy about the certification of Electoral College votes, are complex, and their constitutionality has never been tested. They were the subject of considerable discussion in Bush v. Gore (2000), although the decision in that case did not turn upon them.