"But on the rape thing, it's like, how does putting more violence onto a woman's body and taking the life of an innocent child that's a consequence of this crime, how does that make it better?" Koster said in the exchange.
Koster's campaign manager, Larry Stickney, says the candidate has long been a proponent of dealing strongly with sex offenders. He noted that Koster worked in the state legislature on legislation to crack down on sex offenders and has daughters of his own.
"To imply that he's cavalier about the issue is preposterous," Stickney said.
Koster is locked in a competitive House race against Democrat Suzan DelBene.
Republicans have been beleaguered this year by comments about rape that some have deemed offensive. Rep. Todd Akin, R-Mo., who is challenging Democratic Sen. Claire McCaskill, said women's bodies have ways of avoiding pregnancy in cases of "legitimate rape."
More recently, Indiana GOP candidate Richard Mourdock has been criticized for saying that pregnancy resulting from rape is God's will.
Collin Jergens, a spokesman at the advocacy group FUSE Washington, said one of the group's activists went to the fundraiser to ask Koster about the issue of abortion. Democrats have been trying to portray Koster as out of touch with the district, which stretches from areas east of Seattle to the border with Canada, and they have focused particularly on his stance on social issues.
Sara Kiesler, a spokeswoman for Planned Parenthood Votes Northwest, said the Koster's remarks are proof that he shouldn't be involved in a woman's decision about her pregnancy.
"My gut reaction was that rape is violence, and that rape is a crime, and that his choice of words diminishes that violence," Kiesler said.