Rep. Todd Akin (R-Mo.), the Republican candidate in the race to unseat Sen. Claire McCaskill (D-Mo.), described his opponent as a "dog" that goes to Washington to fetch more regulations and tax burdens.
Akin's description came during a fundraising event in Springfield, Mo., on Saturday, according to local site Politicmo.com, which posted audio from the event.
Akin's comments are only the latest in a race that has been characterized by his controversial statements.
Earlier in the year Akin caught national attention and widespread criticism for saying that a woman's body has natural ways of terminating pregnancies that are the result of "legitimate rape."
He rejected calls from GOP leaders to exit the race, which many Republicans view as critical to their efforts to capture the Senate.
Last month, Akin again received criticism after telling reporters McCaskill was not "ladylike."
Polls before his rape comments showed the candidates locked in a tie, but since then polls have given McCaskill the edge. A poll from Democratic-affiliated Public Policy Polling last week showed McCaskill up 6 points, with 46 percent support to Akin's 40.