Just three times in U.S. history a presidential election has resulted in no candidate getting a majority of electoral votes: 1801, 1825 and 1837. When this happens, Article 2, Section 1, Clause 3 of the U.S. Constitution kicks in—clarified by the 12th and 20th amendments. Basically, the U.S. House of Representatives would vote (by state delegations) to select the President and the Senate (also voting by state delegations) would pick the Vice-President.
Both the 12th and 20th amendments to the constitution determine that this “contingent election” process would take place with the incoming Congress. So, in this scenario, the composition of both chambers is obviously critical to the end result. If Republicans retain the House, Donald Trump would likely become President. And, if Democrats hold on to the Senate, they could pick Tim Walz as Vice-President.
While it’s highly unlikely that the Electoral College will be deadlocked (269 votes for each candidate) or that no candidate gets a majority in some other scenario, it could happen (see the map above). Trump would have to partially break the “Blue Wall” of Midwestern states by taking Michigan and also win Pennsylvania. Harris would have to carry Georgia, Virginia, North Carolina, Arizona, Nevada and New Mexico. Again, all of this is unlikely, but possible given the tightness of the polls in many of these swing states.
So, we could wake up after Election Day (or, more likely, weeks later when it's all tallied) with the first “contingent” presidential election in 187 years! Needless to say, we’d need to fasten our collective seatbelts even more tightly than they are now.