The U.S. House chose Thomas Jefferson on the 36th ballot in the deadlocked presidential election of 1800.
Jefferson and Aaron Burr, both Democratic-Republicans, each received 73 electoral votes because the electoral system then gave every elector two undifferentiated votes. The tie sent the decision to the House of Representatives, where each state delegation cast one vote.
The House began voting in February 1801. Jefferson led eight state delegations, Burr led six, and two delegations were initially divided or unable to choose. The deadlock continued through 35 ballots. On the 36th ballot, several Federalists abstained or shifted their position, allowing Jefferson to win ten state votes.
The episode exposed weaknesses in the original electoral system and helped produce the Twelfth Amendment. Ratified in 1804, that amendment required electors to cast separate votes for president and vice president. Jefferson’s victory also created the first peaceful transfer of national power between rival political parties in U.S. history.