Kamala Harris and Donald Trump are battling for every last vote to secure an advantage in tomorrow’s election. However, there's a slim chance that the U.S. election could end in a tie. This outcome relates to the workings of the U.S. Electoral College, the winner-takes-all system that ultimately decides which candidate will reach the White House.

What if there's a tie?

The Electoral College consists of 538 votes, distributed among the fifty states and the District of Columbia in varying numbers. This setup makes it theoretically possible for a tie between two presidential candidates.

In such a scenario, Harris and Trump could each secure 269 electoral votes, resulting in a complete draw, where neither candidate reaches the majority needed to win the presidency.

This type of stalemate has happened twice in U.S. history, in 1800 and 1824.

In the 1800 election, Thomas Jefferson’s Democratic-Republicans defeated incumbent Federalist President John Adams. At that time, candidates had a 'running mate' from a different state, much like today’s vice-presidential candidates. Electors cast two votes each, with the candidate receiving the most votes becoming president and the runner-up becoming vice president.

This scenario actually occurred in 1824, when Andrew Jackson received 99 electoral votes, John Quincy Adams 84, William Crawford 41, and Henry Clay 37. All candidates were from the same Democratic-Republican Party, which had split into regional factions, as CNN notes.

According to the 12th Amendment, in such cases, the House of Representatives must immediately select the president by ballot from the top three candidates. Each state delegation casts one vote, and a simple majority of states is needed to win.

This process means that Wyoming, the smallest state with fewer than 600,000 people, would have an equal vote to California, which has nearly 40 million residents—even though Wyoming has only three electors while California has 54.

Moreover, the final decision on the presidency would depend on the composition of the House of Representatives, which will be determined in the same election cycle as the presidential race.

How likely is a tie?

Although a tie is unlikely, it remains a possibility, with various scenarios outlined by the site 270toWin.

In one scenario, Trump could win Pennsylvania and Georgia, while Harris claims Wisconsin, Michigan, Arizona, Nevada, and one electoral vote from Nebraska, one of the two states (alongside Maine) that splits its electoral votes.

Another, even less likely scenario has Harris winning all the states that Biden carried, plus North Carolina, which current polls show leaning Republican. If Trump were then to reclaim Michigan, Pennsylvania, and Wisconsin, and win Nevada for the first time, the result would be a 269-269 tie.

This outcome would trigger a “contingent election,” in which the House of Representatives would select the President for the first time in 200 years. A simple majority of 26 state delegations is required to elect the new Commander-in-Chief.

With the nation deeply polarized, incoming members of Congress would face heavy pressure. In some cases, they might have to choose between supporting their party’s candidate or the one with the most popular votes in their state, as state delegations are not bound to follow the winner of their state’s vote.

This process would likely take place on January 6, after Congress confirms that no candidate has a majority, as explained by the Congressional Research Service.

A tie could also lead to a split administration with a Republican president and a Democratic vice president, or vice versa. Under the 12th Amendment, if no majority is reached, the Senate selects the Vice President from the two candidates with the most electoral votes, with each senator casting one vote.

The Senate could elect a vice president even if the House remains deadlocked on the presidency. In this rare scenario, if a president is not chosen by Inauguration Day, January 20, the newly selected vice president would serve as acting president—an outcome few can imagine today.