(CNN) - Saying the decision was "in the best interest of my family," Colorado Gov. Bill Ritter officially announced Wednesday that he will not seek a second term in 2010.
"Over the last years and particularly in this last year, I have attemped to balance many roles in my life," he said. "It is my family that has sacrificed the most."
Ritter, a Democrat who comfortably won a first term in 2006 over Republican Bob Beauprez, was facing a tough re-election battle against former Republican Rep. Scott McInnis. But at an emotional press conference in Denver, Ritter stressed that his decision was "intensely personal" and unrelated to his political fortunes. He said his re-election bid was going well, and argued that the race was "absolutely winnable."
"I don't live and die by polls at all," he said.
Ritter said he did not face any pressure to step aside and let another Democrat run. He also rejected talk that his decision might give Republicans a better shot at winning back the governor's mansion.
"The Democratic party has a very deep bench," he said. "There are a lot of people who are able to step in and do this job. I thought about that. It's not like I didn't make that part of my calculus."
Both the Cook Political Report and the Rothenberg Political Report considered the Colorado governor's race a toss-up. There are 37 governorships are up for grabs in 2010, with Democrats defending 19 and the GOP 18.
Colorado will become the 11th open seat the Democrats have to defend. The Republicans are also defending 11 open seats.