Article II, Section 1 of the original Constitution provided for Electoral College electors to submit single ballots with two names, but no designation of president and vice president. The candidate with the highest total, if a majority, would become president and the second place finisher would become vice president. Each state would have electors equal to the total of senators plus representatives.
Problems developed almost immediately. In 1796, the system yielded a president from one party and a vice president for another. In 1800, two candidates from the same party received the same number of votes, throwing the matter into the House of Representatives where each state would cast a single vote. The emergence of partisan political activity caused the failure of the original constitutional plan.
The 12th Amendment provided the following remedies:
separate ballots are used for president and vice president
the candidates with the greatest number of votes for each office will be elected if that number constitutes a majority of the total electors
if a majority for the president is lacking, the House of Representatives shall vote by state from among the three highest candidates
if a majority for the vice president is lacking, the Senate shall vote by state from among the two highest candidates
the vice president must meet the same constitutional requirements as provided for the president.