What requires electors to vote for a president and Vice President on separate ballots?

The requirement for electors to vote for a president and vice president on separate ballots stems from the 12th Amendment to the U.S. Constitution, ratified in 1804. This amendment was established to prevent confusion and ensure that electors distinctly indicate their choices for each office, thereby reducing the likelihood of electoral disputes. By separating the votes, the amendment clarifies the election process and enhances the integrity of the electoral system.