Colorado prosecutor adds name to list looking to unseat Senator Udall Weld County District Attorney Ken Buck is running for U.S. Senate. The Denver Post reports (http://bit.ly/1cwnOTV) the Republican filed paperwork with the Federal Election Commission on Wednesday indicating he plans to challenge Sen. Mark Udall. Fellow Republicans and state Sens. Randy Baumgardner, of Hot Sulphur Springs, and Owen Hill, of Colorado Springs, also have announced they are seeking Udall's seat. Buck previously ran for Senate in 2010 but lost to Democrat Michael Bennet. Buck's campaign website accuses Udall of being a rubber stamp for President Obama's policies in explaining why he decided to run. Colorado Democratic Party Chairman Rick Palacio said in a written statement that Republicans keep returning to failed ideas and candidates of the past.