Rick Berg, the Republican Senate candidate in North Dakota, speaks in Bismarck, N.D., during a debate with Democratic candidate Heidi Heitkamp. Ms. Heitkamp and Mr. Berg are running for the seat being left open by the departure of incumbent Democrat Kent Conrad, and Mr. Berg is seen as crucial to GOP hopes of capturing control of the Senate. (Associated Press)

Rick Berg, the Republican Senate candidate in North Dakota, speaks in Bismarck, N.D., during a debate with Democratic candidate Heidi Heitkamp. Ms. Heitkamp and Mr. Berg are running for the seat being left open by the departure of incumbent Democrat Kent Conrad, and Mr. Berg is seen as crucial to GOP hopes of capturing control of the Senate. (Associated Press)