In the United States Presidential election of 1800

In the United States Presidential election of 1800, sometimes referred to as the "Revolution of 1800," Vice President Thomas Jefferson defeated President John Adams. The election was a realigning election that ushered in a generation of Democratic-Republican Party rule and the eventual demise of the Federalist Party.

The election exposed one of the flaws in the original Constitution. Members of the Electoral College could only vote for President; each elector could vote for two candidates, and the Vice President was the person who received the second largest number of votes during the election. The Democratic-Republicans had planned for one of the electors to abstain from casting his second vote for Aaron Burr, which would have led to Jefferson receiving one electoral vote more than Burr. The plan, however, was bungled, resulting in a tied electoral vote between Jefferson and Burr. The election was then put into the hands of the outgoing House of Representatives controlled by the Federalist Party. Most Federalists voted for Burr in order to block Jefferson from the Presidency, and the result was a week of deadlock. Federalist Alexander Hamilton, who detested both but preferred Jefferson to Burr, intervened on Jefferson's behalf, which allowed Jefferson to ascend to the Presidency. Hamilton's actions were one cause of his duel with Burr, which resulted in Hamilton's death in 1804.

Jefferson and Burr tied for first place, so the election was thrown into the House of Representatives.

The members of the House of Representatives balloted as states to determine whether Jefferson or Burr would become President. There were sixteen states, and an absolute majority—in this case, nine—was required for victory.

While it was common knowledge that Jefferson was the candidate for President and Burr for Vice President, the lame-duck House was controlled by the Federalists, who were loath to vote for Jefferson (with one exception, Alexander Hamilton), their partisan nemesis; Jefferson was the key opponent of Federalists since 1789. Seizing a chance to elect Burr as opposed to Jefferson, most Federalists voted for Burr, giving Burr six of the eight states controlled by Federalists. The seven states controlled by Democratic-Republicans all voted for Jefferson, and Georgia's lone living Federalist representative also voted for Jefferson, giving Jefferson eight states. Vermont was evenly split, casting a blank ballot. The remaining state, Maryland, had five Federalist representatives to three Democratic-Republicans; one of its Federalist representatives voted for Jefferson, forcing the state delegation to cast a blank ballot.

Over the course of seven days from February 11 to February 17, the House cast a total of 35 ballots, with Jefferson receiving the votes of eight state delegations each time—one short of the necessary majority of nine. During the confusion, Alexander Hamilton said he supported Jefferson because he was “by far not so dangerous a man” as Burr; in short, he would much rather have someone with wrong principles than someone devoid of any. Hamilton embarked on a frenzied letter-writing campaign to get delegates to switch votes. He narrowly succeeded, and on Tuesday, February 17, on the 36th ballot, Jefferson was elected.

Federalist James A. Bayard of Delaware and his allies in Maryland and Vermont all cast blank ballots. This resulted in the Maryland and Vermont votes changing from no selection to Jefferson, giving him the votes of 10 states and the presidency. Bayard, as the sole representative from Delaware, changed his vote from Burr to no selection. The four present representatives from South Carolina also changed their 3-1 selection of Burr to four abstentions. The final count was Jefferson with ten votes to Burr's four.