Electoral College Ties
Note that the discussion on this page is mostly written around a 269-269 tie between two candidates. However, much of the same would come into play if a third party candidate wins enough electoral votes to prevent any candidate in the race from reaching 270.
Game it out: Electoral College Tie Finder 3rd Party Interactive Map
It takes 270toWin. If neither candidate gets a majority of the 538 electoral votes, the election for President is decided in the House of Representatives, with each state delegation having one vote. A majority of states (26) is needed to win. Senators would elect the Vice-President, with each Senator having a vote. A majority of Senators (51) is needed to win.
State House delegations can cast their vote for president from among the three candidates receiving the most electoral votes, while Senators are limited to the top two candidates in their vote for Vice-President.
It is important to note that an apparent tie on election night does not mean that there is actually a tie. The Electors meet on the first Monday after the second Wednesday in December (December 19, 2016) to cast their votes. Only about half the states have laws requiring their Electors to vote for the popular vote winner. It is possible that an Elector could cast his or her vote for another person. An Elector casting his or her vote this way is known as a faithless Elector.
In a 269-269 tie, as long as that rogue vote wasn’t for the other major candidate in the race, this wouldn’t be an issue. Both candidates would still be short of the required 270. However, imagine a scenario where a single Elector in a single state switched their vote to the other candidate in the tie --- the vote would be 270 to 268. While very unlikely, this kind of vote has happened before (most recently in 1968, although the electoral vote that year wasn’t close).
More than likely, the election would remain undecided after the Electors voted. The Congress meets in joint session on January 6, 2017 to count the electoral votes (this count happens whether the election is close or not). If no candidate has reached 270 Electoral Votes, then the House and Senate take over and elect the President and Vice-President, respectively. Note that the newly elected Congress will be sworn in on January 3rd, 2017. It is that new Congress that takes on this responsibility.
Who would win the presidency in a tie?
Each state's Congressional House delegation would have one vote, regardless of how many Districts are in the state. The following is a summary from September, 2016, based on projections for that November.
At the time, the best case scenario for Democrats was a 24-24 split, with two ties. Getting there, however, would require a huge 'wave' election. In that case, we wouldn't be dealing with a tie in the electoral vote.