An embattled Republican incumbent, Mia Love, is in a tight race with her Democratic challenger, Ben McAdams. Ms. Love, the lone black Republican woman in Congress, is battling accusations that she raised campaign funds improperly during her primary election; she has acknowledged some errors but characterized the allegations as a politically motivated attack. Mr. McAdams, the mayor of Salt Lake County and a former state senator, has seized on the accusations and held them up as an example of a culture of corruption in Washington that he promises to combat. The race is regarded as a toss-up.