The election of 1800 was decided in the House of Representatives due to a tie in the Electoral College between Thomas Jefferson and Aaron Burr. Both candidates, representing the Democratic-Republican Party, received 73 electoral votes, while the Federalist candidate, John Adams, received 65 votes, and another Federalist, Charles Cotesworth Pinckney, received 64 votes.
Under the rules established by the Constitution, when no candidate receives a majority of the electoral votes, the decision goes to the House of Representatives. Each state delegation in the House casts one vote for one of the tied candidates, and a majority of state votes is required to win. In this case, it took 36 ballots in the House to finally elect Jefferson as president after intense political maneuvering and negotiation.
The election highlighted the flaws in the electoral system of the time, leading to the passage of the Twelfth Amendment in 1804, which established a separate ballot for presidential and vice-presidential candidates to prevent such ties in the future.