(NEXSTAR) — Former President Donald Trump is projected to have won his 2024 bid to reclaim the White House, while the Senate has predictably flipped to a Republican majority.

But when it comes to control of the House, the citizens of the U.S. may not know the outcome for days, or perhaps weeks.

Dozens of House races have yet to be called, in part because of close races in many districts, but also because of the differing processes for voting, counting and releasing the results in different states. For instance, California, where several key races have yet to be called, is consistently among the slowest to report all of its election results. 

California, which has long had a culture of voting absentee, started moving toward all-mail elections last decade. All-mail systems will almost always prolong the count. Mail ballots require additional verification steps — each must be opened individually, validated and processed — so they can take longer to tabulate than ballots cast in person that are then fed into a scanner at a neighborhood polling place.

“Our priority is trying to maximize participation of actively registered voters,” Democratic Assemblymember Marc Berman, who authored the 2021 bill that permanently switched the state to all-mail elections, said earlier this year. “What that means is things are a little slower. But in a society that wants immediate gratification, I think our democracy is worth taking a little time to get it right and to create a system where everyone can participate.”

In the past five general elections, California has tabulated an average of 38% of its vote after Election Day. Two years ago, in the 2022 midterm elections, half the state’s votes were counted after Election Day.

Among other states with close races for seats in the House, Washington and Oregon — both of which operate a vote-by-mail system — will also likely not have final results until well after Election Day, as votes can be postmarked as late as Election Day, The Hill reported.

Increasingly close races in the House also contribute to a more lengthy tabulation process, especially when no frontrunners emerge during early results.

“There are only so many purple districts left, and in those purple districts — boy, are they really purple. The margins are very, very narrow,” a Democratic strategist told The Hill prior to Election Day.

None of this comes as much of a shock to election officials. The midterm elections in 2022 proved that control of the House could be determined well after voting has finished. That year, the races were finally called — and the GOP secured a majority — more than a week after Election Day.

The Associated Press contributed to this report.