Colorado Gov. Bill Ritter won't run for re-election this fall, sources told The Associated Press on Tuesday.
The first-term Democrat was elected in 2006 in a pivotal swing-voting state. He has been widely considered a rising star in the Democratic Party.
Two Democrats with knowledge of Ritter's decision disclosed it on the condition of anonymity because they weren't authorized to publicly discuss the governor's political plans.
Ritter did not return phone calls seeking reaction. Sources said Ritter called a news conference on Wednesday to announce his decision. A spokesman for Rep. Diana DeGette, D-Colo., said she and Pat Waak, the state Democratic Party chairmwoman, would call a meeting of senior elected officials from Colorado on Wednesday to discuss how to go forward as a party.
Reaction from Republicans was swift.
"What a dramatic turn of events. He was a very weak incumbent and he wanted to get out on his own terms," said Republican Party Chairman Dick Wadhams.
Top contenders to replace Ritter included Denver Mayor John Hickenlooper, Interior Secretary Ken Salazar and former House Speaker Andrew Romanoff.
GOP gubernatorial candidate Scott McInnis told The Associated Press that polls showed Ritter was too weak to survive a general election.
"He was in severe trouble. This guy could not win re-election," McInnis told The Associated Press.
"What is their plan B?" he asked.
McInnis said Romanoff has youth and Hickenlooper has charisma, but both are from Denver and he said Colorado needs more.
He said Romanoff was struggling in his U.S. Senate campaign and he would have more support in a gubernatorial race.
McInnis said Hickenlooper's Achilles heel is his record and his support for taxes.
GOP political consultant Katy Atkinson said all three Democratic opponents would be formidable challengers.
Two Republicans are seeking the GOP nomination: McInnis and businessman Dan Maes.
Sidoti reported from Washington.