Millions of Californians have not yet returned their vote-by-mail ballots, and county election officials say the flood of returns expected on Tuesday could delay results in tight races.
As of Monday morning, many counties had received only about half of the absentee ballots they had mailed out.
More than 7.6 million absentee ballots were requested statewide for the general election. In some counties, vote-by-mail is expected to exceed in-person voting.
That means a huge number of last-minute returns will not be counted on election night, and the most competitive races may remain too close to call.
Experts say turnout this year will likely hover around 60 percent, similar to past midterm elections, but significantly lower than 2008.