Seven Senate Republicans face challengers in the 2014 primaries, complicating the party's solid shot at taking majority control away from Democrats. Here's a look at the races:
Senate Minority Leader Mitch McConnell, who is bidding for a sixth term with the possibility of the ultimate prize of majority leader, faces tea party-backed businessman Matt Bevin. McConnell has spent some of the millions he's raised criticizing Bevin on tax payments. Primary is May 20.
Sen. John Cornyn, who as party whip is second in the GOP Senate leadership, got a last-minute challenge from Rep. Steve Stockman. Stockman is casting Cornyn, a two-term conservative, as too liberal. Stockman lacks Cornyn's fundraising and faces an uphill fight in a state where Sen. Ted Cruz stunned the establishment in 2012. Primary is March 4.
Three-term Sen. Pat Roberts is facing Dr. Milton Wolf, a distant cousin of President Barack Obama who has made criticism of the health care law a premier issue in his campaign. Wolf faults Roberts for backing Kathleen Sebelius, former Kansas governor, as health and human services secretary. Roberts has called for Sebelius to resign. Primary is Aug. 5.
Six-term Sen. Thad Cochran insists he's not ready to retire at age 76 and Mississippi's establishment is rallying around the incumbent, a former Appropriations Committee chairman who could assume that post again. State Sen. Chris McDaniel, 41, has the backing of several outside conservative groups. Primary is June 3.
Two-term Sen. Lindsey Graham, who has worked with Democrats on an immigration overhaul and other issues, faces several candidates: state Sen. Lee Bright, small business owner Richard Cash and Nancy Mace, the first woman to graduate from South Carolina's military college, The Citadel, in 1999. If no candidate gets 50 percent of the vote in the June 10 primary, a runoff is held June 24.
Senate Republicans have rallied around three-term Sen. Mike Enzi, who faces a challenge from Liz Cheney, daughter of former Vice President Dick Cheney. She moved her family from Virginia to Wyoming to run for the seat, upsetting some Republicans. Primary is Aug. 19.
Two-term Sen. Lamar Alexander faces state Rep. Joe Carr among several other challengers. Carr has called Alexander the most liberal member of the state's GOP delegation in Congress. Primary is Aug. 7
Sens. Jim Risch of Idaho, Susan Collins of Maine, Jeff Sessions of Alabama, Jim Inhofe of Oklahoma and Tim Scott of South Carolina have no challenger at this stage. Sens. Mike Johanns of Nebraska and Saxby Chambliss of Georgia are retiring.
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