Newsom's campaign says he raised more than $5 million from January to June - double each of his chief Democratic rivals. He was the first to launch a gubernatorial campaign.
Financial reports filed Monday show Democrat John Chiang, the state treasurer, raised $2.6 million in the first half of 2017. Former Los Angeles Mayor Antonio Villaraigosa brought in $2.3 million.
Republican John Cox contributed $3 million to his own campaign and raised about $200,000 from other sources.
The top two June primary finishers will advance to the general election regardless of party.
The 2018 governor's race will be the first in eight years without an incumbent running.
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