Question

Why did the House of Representatives decide the presidential election of 1800

Answer 1

Before the 12th amendment in 1804, electors in the Electoral College cast two votes each. The candidate with the most votes became president, the second highest vote getter became vice president. The Democratic-Republicans clearly won the election and their two candidates would get the most votes. An arrangement was made so that one elector would only use one vote and cast it for Thomas Jefferson, making him president. Aaron Burr would get one less vote and become Veep.
But every one of their electors cast one vote for Jefferson and one for Burr. The resulting tie in the EC threw the election to the House in accordance with the Constitution. The House had to vote 35 times before giving TJ the presidency and Veep to Burr.
The 12th amendment required EC electors to vote for each office by name.