The Senate has a mechanism to break ties, but it's not clear whether it applies to the case of choosing a vice president. The House, however, has no such tie-breakers. If the House falls short of the 26 state-delegation votes needed to elect a president, members must keep balloting until a deal is brokered, a compromise is reached, or a state switches its vote.
In a polarized and litigious campaign cycle, the obstacles to an agreement on an issue as important as the choice of president and vice president would be fierce, ranging from procedural obstruction within the House and Senate to outside litigation to delay or block a result.
At the same time, intense negotiating between political parties and among members of Congress could also produce a solution. As in 2001, a senator may opt to switch parties in a 50-50 Senate in exchange for a committee chairmanship, tipping the majority. The compromise could also be epic: In the disputed election of 1876, for example, Republicans agreed to end Reconstruction and pull federal troops out of the South in exchange for an agreement to choose Rutherford Hayes, the loser in the popular vote, to be president – a decision with long-term consequences for race relations in the United States.
There's already talk on Capitol Hill of the possibility of a senator switching parties in the event of another 50-50 Senate.
If the House is unable to choose a president by noon on Inauguration Day, Jan. 20, then the new vice president becomes the acting president, until the House can find 26 state delegations able to agree on an outcome.
If both the House and Senate fail to choose a president and vice president, the House speaker could become acting president, until the issue is resolved. If the speaker declines to permanently give up the speakership, as required, the next in line would be the president pro tem of the Senate, typically the most senior member of the majority party. If Democrats hold their majority, the president pro tem would be Sen. Daniel Inouye (D) of Hawaii. Should Republicans win control of the Senate, Sen. Orrin Hatch (R) of Utah could get the nod.
Curiously, the No. 1 Senate leader, majority leader Harry Reid (D) of Nevada, is not in line to be interim president. That's because the office of majority leader didn't evolve until the 20th century and is not included in the Constitution.