Both Jefferson and Burr tied in the electoral college. They were on the same ticket and were both Republicans. Jefferson was intended to be the president and Burr the vice president, but before the 12th amendment the electoral votes did not distinguish between the two. Electors were voting for both to become president. Because they tied the House of Representatives could have voted Burr president and embarrass Jefferson. They tried and almost succeeded. To prevent this to happen again they passed the 12th amendment.