Former Gov. Bill Ritter on Tuesday endorsed Diane Mitsch Bush, one of three Democrats running for the 3rd Congressional District seat held by four-term U.S. Rep. Scott Tipton, maintaining that the former state representative is the only candidate who can oust the incumbent Republican.

Noting that he first met Mitsch Bush in 2006, when he was running for governor and she was a Routt County commissioner, Ritter said in a statement: “Unlike so many today, Diane has a unique ability to relate to people of all walks of life, listen to voters and work tirelessly to solve constituents’ problems.”

Ritter, the director of Colorado State University’s Center for the New Energy Economy, praised Mitsch Bush as a longtime champion of the environment.

“Diane is the pioneering, forward-thinking, environmental steward we need to protect our home, Colorado’s way of living, and our economic foundation,” he said.

But it was her ability to win a Republican-held seat and win by wide margins in a district where Democrats were outnumbered by Republicans and unaffiliated voters that sealed it for Ritter.

“Diane is the candidate of the people and the only one who can turn Colorado’s 3rd Congressional District blue again,” Ritter said.

Mitch Busch is running in the June 26 primary against attorney Karl Hanlon and former Eagle County Commissioner Arn Menconi, the Green Party nominee for Colorado’s U.S. Senate seat two years ago.