1804 – The 12th Amendment to the U.S. Constitution was ratified. With the amendment, Electors were directed to vote for a President and for a Vice-President, rather than for two choices for President.

The Electors shall meet in their respective states and vote by ballot for President and Vice–President, one of whom, at least, shall not be an inhabitant of the same state with themselves; they shall name in their ballots the person voted for as President, and in distinct ballots the person voted for as Vice–President, and they shall make distinct lists of all persons voted for as President, and of all persons voted for as Vice-President, and of the number of votes for each, which lists they shall sign and certify, and transmit sealed to the seat of the government of the United States, directed to the President of the Senate;the President of the Senate shall, in the presence of the Senate and House of Representatives, open all the certificates and the votes shall then be counted;The person having the greatest number of votes for President, shall be the President, if such number be a majority of the whole number of Electors appointed; and if no person have such majority, then from the persons having the highest numbers not exceeding three on the list of those voted for as President, the House of Representatives shall choose immediately, by ballot, the President

Constitution.congress.gov