Millions of Americans will follow election returns on Tuesday night, but the complete results are unlikely to be known by the time the day ends. Experts say counting and certification could take days or, in some states, weeks.

Maine, Alaska, Arizona and California are among the states where delayed results could affect the balance of power in Congress. It may not be clear before the end of election night which party controls the House and Senate, although the House could be decided sooner because several key Senate contests are expected to remain close, including races in Alaska and Maine.

The delays can result from the number of ballots, geographic challenges and state rules governing when mail ballots may be received and counted. Maine and Alaska also use ranked-choice voting, a system that can extend the process.

Slow counts are not unique to the United States, but prolonged uncertainty can frustrate candidates and voters. In recent years, delays have also provided an opening for politicians, particularly President Trump, to make unsubstantiated claims of fraud.

Trump made similar claims after the 2020 election, when large numbers of mail ballots supporting Joe Biden were counted after Election Day. He revived that criticism in June after California’s primary, alleging that Democrats had engaged in “BIG cheating” and questioning the delay in counting votes.

There was no evidence of cheating in the California primary. However, it took six days to determine the result of the Los Angeles mayor’s race and seven days to call the gubernatorial contest.

Sources: The New York Times Politics.