Sen. Ben Nighthorse Campbell, R-Colo., was one of the first, deciding in 2004 that it would be more fun to ride his tricked-out Harley than run for re-election. Voters promptly replaced him with Democrat Ken Salazar.
Wayne Allard, like Campbell a Coloradan , and Pete Domenici of New Mexico are the most recent. Each is a Republican, each is retiring this year, and each is giving up a Senate seat that Democrats say they can capture.
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