Who will be the US president if election results are unknown by January 20 in 2021

Article II, Section I of the U.S. Constitution states that a president is elected to serve a four-year term. The current presidential term officially ends on January 20, 2021. Even if the election results are not finalized by that date, President Donald Trump (R) will no longer be president, and Vice President Mike Pence (R) will no longer be vice president. What happens next would depend on several factors.

In one scenario, the results of the presidential election would be unknown because no candidate received a majority of the vote in the Electoral College. In that case, the Twelfth Amendment to the U.S. Constitution holds that the House of Representatives elects the president, and the Senate elects the vice president. If the House fails to elect a president by March 4, 2021, the Twelfth Amendment requires that the vice president assume the office of president.

In a second scenario, the question of whether a candidate has won the Electoral College is taken up in the courts, and the issue remains unresolved past January 20. The outcome depends on whether a new Congress has been sworn in by January 20.

If a new Congress has been sworn in, the next in line would be the speaker of the House of Representatives, currently Nancy Pelosi . If a new Congress has not been sworn in by January 20, there would be no serving House. There would be a partial Senate, however, made up of the 65 senators whose seats were not up for election. After the speaker of the House, the next in line to serve as president is the president pro tempore of the Senate. In a partial Senate, Democrats would hold a majority with 35 seats and control the chamber. The most senior member of the majority party—Sen. Pat Leahy  in this scenario—would become president pro term and serve as acting president.

Another possibility is that a partial new Congress would be sworn in while the rest of the election results were being finalized. There is no precedent for this, and it is unclear how it would operate. Any of these situations would likely lead to court challenges. The nearest the U.S. has ever come to being without a president on Inauguration Day was in 1876. More in ballotpedia.org