The Twelfth Amendment, adopted in 1804 after two chaotic elections, created the modern running mate system by requiring electors to cast separate ballots for president and vice president. Under the original Electoral College, electors voted for two candidates on the same ballot for president, with the second-place finisher becoming vice president. This system broke down in the 1800 election when the House of Representatives had to choose between running mates Thomas Jefferson and Aaron Burr, who tied in electoral votes. The amendment mandates that one of each elector''s votes must go to someone from a different state than the elector, effectively preventing presidential candidates from selecting running mates from their home state without losing electoral votes. Modern presidential campaigns choose running mates to appeal to different voter demographics. The system formalized during the Civil War era, establishing the joint ticket approach where president and vice president run together as a unified campaign rather than as competitors.