State Rep. Stace Nelson, left, a Republican candidate for U.S. Senate, and Democratic candidate Rick Weiland speak at a joint news conference, Monday, April 7, 2014, in Sioux Falls, S.D. The candidates criticized former Gov. Mike Rounds, the Republican frontrunner in the race, for his millions of dollars raised from out-of-state sources. (AP Photo/Dirk Lammers)