That could be a problem for Republicans in other state races, but an expert in voter turnout says it likely won't be.
George Mason University political science professor Michael McDonald runs the United States Elections Project. He says the lack of a competitive race will likely hurt Republican enthusiasm--a bit.
"There will be a dampening, but it won't be a huge drop-off of Republican turnout," McDonald says. "There's still the state elections on the ballot, and there's still going to be residual interest for voters to express their interest in Trump."
McDonald points out that, in other states, voters cast ballots for candidates who had already pulled out of the race.
But a drop in Republican votes could hurt the party in state races, where Democrats and Republicans run against each other and the top two vote-getters advance, such as in the election for California's open U.S. Senate seat.
McDonald thinks the drop in turnout won't be large enough to sway many races.
"You probably still are going to see higher turnout than you normally do for a primary election in California," McDonald says.
The Public Policy Institute of California reports the state's voter turnout has ranked in the top 10 in every presidential primary since 1980.
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