What was the outcome of the presidential election of 1800?

The presidential election of 1800 was notable for being the first partisan contest in American political history. The campaign was extremely bitter and rancorous, with insults, smears, and personal abuse very much the order of the day. The two candidates were the sitting president John Adams, representing the Federalists, and his Republican Vice President Thomas Jefferson. Adams and Jefferson heartily detested each other, which accounted for the deeply personal tenor of this hard-fought campaign.
It was generally thought a foregone conclusion that Adams would lose. He was a deeply unpopular president, accused by his Republican opponents of wanting to turn himself into a king. President Adams had signed into law a number of draconian measures such as the Alien and Sedition Acts, which had, among other things, restricted free speech in the name of national security. Republicans were outraged at these measures, seeing them as an attack on the cherished tradition of American liberty. No wonder they thought that Adams wanted to establish himself as another King George III.
As expected, Jefferson and his running-mate Aaron Burr won the election. However, due to the unusual system in force at that time, the House of Representatives had to decide which of the two would become president, as they were tied in the Electoral College. As the outgoing House had a Federalist majority—the party of Adams that had just lost the election—Jefferson and his supporters feared that his opponents would use their majority in the House to deny him the presidency.
After a lengthy process, with involved all kinds of deals being conducted behind closed doors, Jefferson was finally declared the winner. This was due in no small part to the tireless efforts of the arch-Federalist Alexander Hamilton. Hamilton had no time for Jefferson but regarded him as a less dangerous figure than Burr, who would in due course become a danger to Hamilton on a much more personal level.