The GOP previously had donated $200,000 to Blakeslee's bid to win the Senate seat vacated by Abel Maldonado's selection for lieutenant governor. The coastal district stretches from Santa Cruz and Santa Clara counties south to Santa Barbara.
Blakeslee, R-San Luis Obispo, finished ahead of former Democratic Assemblyman John Laird of Santa Cruz in a June 22 primary election, but the Republican legislator fell just short of the majority needed to capture the seat outright.
Blakeslee, Laird and two minor-party candidates - Libertarian Mark Hinkle and independent Jim Fitzgerald - will square off Aug. 17 in a runoff election.
The race is considered crucial because Maldonado is a Republican and if Democrats succeed in capturing his former seat, they would control 26 of 40 Senate seats, just one less than the two-thirds majority necessary for the house to pass a budget or new taxes.
Before voters went to the polls in last month's primary, more than $2 million had been poured into the race, either through campaigns or independent expenditures by interest groups.
File photo by Bee photographer Hector Amezcuz.