The Seattle Times reported that Koster in a letter to supporters said the national and state Republican party only provided token support.
State GOP Chairman Kirby Wilbur contested Koster's assessment, saying Koster's team ran a horrible campaign that did not meet fundraising targets set by the National Republican Congressional Committee.
Koster conceded Friday to Democratic candidate Suzan DelBene, who led with 53 percent of the vote.
DelBene, a former Microsoft executive, dumped $2.8 million of her own money into her campaign.
Koster, a Snohomish County Council member, is a longtime social conservative who embraced the tea-party movement and, like other national Republicans, made controversial comments about rape and abortion.
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