


** FILE ** In this March 31, 2012, photo, Rep. Rick Berg, North Dakota Republican, speaks before the North Dakota GOP Convention in Bismarck, N.D. Berg is running for the Senate seat being vacated by Sen. Kent Conrad. (AP Photo/Will Kincaid, File)

Mitt Romney, the presumptive GOP presidential nominee, delivers the commencement address at Liberty University in Lynchburg, Va., on Saturday. (Associated Press)

Mitt Romney, the presumptive GOP presidential nominee, delivers the commencement address at Liberty University in Lynchburg, Va., on Saturday. (Associated Press)

Mitt Romney, the presumptive GOP presidential nominee, delivers the commencement address at Liberty University in Lynchburg, Va., on Saturday. (Associated Press)

Sen. Richard G. Lugar of Indiana exits after delivering his GOP primary concession speech in Indianapolis on Tuesday night. The 80-year-old Republican was defeated in his bid for a seventh six-year term, to the delight of many tea party activists. (Associated Press)

Sen. Richard G. Lugar of Indiana exits after delivering his GOP primary concession speech in Indianapolis on Tuesday night. The 80-year-old Republican was defeated in his bid for a seventh six-year term, to the delight of many tea party activists. (Associated Press)

Former Massachusetts Gov. Mitt Romney, the presumptive GOP presidential nominee, speaks at a campaign stop at KP Kauffman Co., an oil and gas production and drilling company, in Fort Lupton, Colo., on Wednesday, May 9, 2012. (AP Photo/Jae C. Hong)

Sen. Richard G. Lugar, Indiana Republican, is video recorded by a cell phone during a visit to the West Lafayette wastewater treatment center Monday, May 7, 2012 in West Lafayette, Ind. Lugar lost Tuesday's GOP primary election to tea party candidate Richard Mourdock. (AP Photo/Journal & Courier, Michael Heinz)

Sen. Richard G. Lugar of Indiana is fighting to win the GOP nomination for a seventh term in the Senate against Richard Mourdock, the tea party-backed state treasurer who argues the senator is too moderate for the state. (Associated Press)