Twelfth Amendment to the United States Constitution

Amendment XII (the Twelfth Amendment) of the United States Constitution, which details a new system for presidential elections, was motivated by the Presidential election of 1800. Prior to ratification of the Twelfth Amendment, votes for President and Vice President were not listed on separate ballots. Thomas Jefferson and his running mate Aaron Burr tied in the number of electoral votes received, neither receiving a majority of votes. The House of Representatives voted over thirty times to a tie vote before a deal was struck and Jefferson was elected.

The amendment itself was a subject of a constitutional dilemma. On June 15, 1804, the amendment received the constitutionally-required ratification by three-fourths of the state legislatures when New Hampshire ratified the amendment. However, on June 20, the Governor of the state vetoed the amendment. Since the Constitution doesn't mention anything about governors, it's questionable whether their veto matters. The issues was resolved when Tennessee ratified the amendment on July 27, 1804.

The full text of this amendment can be found here (http://www.archives.gov/exhibit-hall/charters-of-freedom/constitution/amendments-11-27.html#12).