If no candidate reaches 270 electoral votes, the House of Representatives and Senate will determine the occupant of the White House.
In the House, each state delegation gets one vote to elect the president, whether it's a state with a larger population like California or a smaller state like Wyoming. Meanwhile, each senator will choose who will become vice president. Theoretically, both chambers could elect a president and vice president from opposing parties.
If the House of Representatives fails to elect a president on Inauguration Day, the vice president-elect will act as acting president.
In the event of a 25-25 tie in the House and a tie in the Senate, the Presidential Succession Act of 1947 provides that, at least temporarily, the Speaker of the House becomes president. Nonetheless, the chambers were instructed to continue voting until ties were broken.