The Twelfth Amendment

Under the original Article II, each elector cast two votes for President, and the runner-up became Vice President. The system failed once parties emerged. In 1796 it produced a President and Vice President from rival parties, John Adams and Thomas Jefferson, and in 1800 Jefferson and his running mate Aaron Burr each received 73 electoral votes, throwing the election to the House of Representatives, where Federalists nearly blocked Jefferson. The House chose Jefferson on its 36th ballot, on February 17, 1801.

Congress proposed the Twelfth Amendment on December 9, 1803, and it was ratified on June 15, 1804, in time for that year's election. It requires electors to cast distinct ballots for President and Vice President. If no candidate wins a majority of electoral votes for President, the House chooses among the top three, with each state delegation casting one vote, and if no one wins a majority for Vice President, the Senate chooses between the top two. It also requires the Vice President to meet the same qualifications as the President.

The House has chosen the President only once under the amendment, selecting John Quincy Adams in 1825, and the Senate has chosen the Vice President once, Richard Mentor Johnson in 1837. The amendment also bars electors from voting for both a presidential and a vice presidential candidate from their own state, a rule that drew attention in 2000 when Dick Cheney changed his residence from Texas. Its procedures for counting electoral votes, and the role of the Vice President in that count, were central to the disputes after the 2020 election and to the Electoral Count Reform Act of 2022.