Thirteen candidates are running for the U.S. Senate seat being vacated by retiring Idaho Sen. Larry Craig, as absentee voters have begun marking their ballots for the state’s May 27 primary.

Eight Republicans, two Democrats, two independents and a Libertarian are vying for the chance to replace Craig.

Lt. Governor Jim Risch, who served as governor for seven months when Dirk Kempthorne was named Interior Secretary, is considered the front-runner in the Republican primary - his campaign co-chairs are Senator Mike Crapo and former Governor Phil Batt, and he has endorsements from the state GOP party chairman and governor.

Other Republican candidates are Post falls businessman Richard Phenneger; Wilder real-estate broker and Army Reserve colonel Scott Syme; former Idaho National Lab attorney Fred Adams; McCall electrical engineer Neal Thompson; Sweet machinist Brian Hefner; Las Vegas civil engineer Bill Hunter, who recently moved back to his family home in southeastern Idaho; and California real estate broker who has never been to Idaho. By law, Senate candidates are required only to reside in the state on the date of the November election.

On the Democratic ticket, former two-term Congressman Larry LaRocco will square off in the primary against Fort Hall tribal court advocate David Archuleta.

Also running are Libertarian Kent Marmon, and independents former elk rancher Rex Rammell and Pro-Life, whose name was legally changed from Marvin Richardson.