A string of too-early-to-call California U.S. House races remains in play and might end up determining whether Republicans seize control or Democrats hang on to power.

With millions of votes still uncounted Wednesday across the nation’s most populous state, uncertainty remained for about a dozen of the state’s 52 House contests. The most competitive of those races were in the Los Angeles region and the Central Valley farm belt.

In Southern California, Democratic Reps. Katie Porter and Mike Levin were locked in close races, despite President Joe Biden’s late-hour campaign swing on their behalf. East of Los Angeles, Republican Rep. Ken Calvert was trailing Democrat Will Rollins by 12 points, but less than one-third of the anticipated votes had been tallied.

In the Central Valley, GOP Rep. David Valadao, who voted to impeach then-President Donald Trump, had 54% of the votes counted so far in his race against Democrat Rudy Salas, but most ballots had yet to be tabulated. Four years ago, Valadao lost a reelection bid after seeing a sizable lead on election Day evaporate as late-arriving mail-in ballots were counted. He won back the seat in 2020.

Should Democrats defeat Calvert and prevail in other contests where they were leading or only slightly behind, the year would have echoes of 2018, when the party seized seven Republican-held California seats on the way to retaking the House.

But if Calvert hangs on and Republicans oust Porter and Levin and win an open seat in Central California, the scenario would look similar to 2020, when GOP House candidates flipped four seats in a state where registered Democrats outnumber Republicans by nearly 2-to-1.