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California’s Democratic congressional candidates amassed an enormous cash advantage over their Republican rivals over the summer as money poured into the state’s most competitive races, potentially spelling trouble for many red-district incumbents in the final weeks before Election Day.

The fund-raising gaps, detailed in new quarterly Federal Election Commission finance reports, are especially noteworthy in tossup districts where get-out-the-vote efforts are crucial but can also be costly and labor intensive.

Here’s an overview of fund-raising in California, between July 1 and Sept. 30:

• 10th District: Josh Harder, a Democrat, raised more than $3.5 million while the incumbent Republican, Representative Jeff Denham, raised $650,000.

• 21st District: T.J. Cox, a Democrat, raised $900,000 while Representative David Valadao raised $600,000.