What caused the 12th amendment?
After the 1800 Presidential Election, the 12th Amendment was adopted to fix a flaw in the Constitution that had allowed Thomas Jefferson to tie in the Electoral College with his vice presidential candidate Aaron Burr. The election was then sent to the House of Representatives, which required 36 ballots to finally elect Jefferson president. The 12th Amendment specifies that electors shall cast distinct votes for the president and vice president, rather than electoral votes for two men.