In some states, more people are on track to cast ballots in early voting than in the entire election in 2014. In Texas, one such state, hundreds of thousands of new voters have already participated. Democrats hope that surge indicates that their Senate candidate, Beto O'Rourke, may be succeeding in mobilizing a crucial demographic.

But Republicans are also energized, turning out in larger numbers than Democrats so far in Florida, for example, where a cliffhanger race for governor features a Donald Trump acolyte competing against a progressive who would be the state's first African-American governor.

The picture in California so far is more status quo. The state has at least a half dozen hotly contested congressional districts, which could play a big role in whether Democrats take back a majority in the House. But in the rest of the state, the lack of a close race at the top of ticket is holding down turnout, said Paul Mitchell, vice president of Political Data, which compiles voter data in the state.

California was one of the country's pioneers in widespread early voting, and at this point, a large majority of voters get their ballots in the mail and either send them back or drop them at a polling station. About 3 million ballots were cast in the state by Friday.