Steven Roberts II filed his lawsuit in St. Louis Circuit Court Thursday, two days after a special prosecutor declined to pursue charges in the case, saying the evidence doesn't support Cora Faith Walker's claims.
Walker, who is married, alleges Roberts sexually assaulted her when they met at an apartment in August to discuss how they could work together in the upcoming legislative session. Both Democrats are running unopposed for the Missouri House.
Roberts has said he and Walker had consensual sex.
Walker didn't return Associated Press telephone messages seeking comment Friday.
The lawsuit seeks at least $25,000 in damages on each count of defamation, malicious prosecution and inflicting emotional distress.
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