Buck to Enter U.S. Senate Race By Bente Birkeland • Aug 8, 2013 ShareTwitter Facebook Google+ Email Ken Buck campaign site photo (cropped). Republican Weld county district attorney Ken Buck plans to challenge Democratic U.S. Senator Mark Udall next year. Buck filed the paperwork today and as Bente Birkeland reports, he’ll first need to win the Republican primary. Listen Listening... / Tags: ElectionsnewsroomCapitol CoverageView the discussion thread.