DENVER -- Former GOP congressman Tom Tancredo is in the race for governor.

Tancredo had given the two Republican candidates a noon deadline to withdraw from the Republican ticket if polls showed the primary winner was behind Democratic Denver Mayor John Hickenlooper. If they didn't, he said he would jump into the race as a third-party candidate.

At 12:30 p.m., Tancredo confirmed he is seeking the nomination of the American Constitution Party, as their candidate for governor.

"That is my goal. That is my absolute desire," Tancredo told 7NEWS. "I don't want Mayor Hickenlooper to be governor."

"I think I have a better chance of winning in a three-way race than either one of the two Republican candidates have today in a two-way race," he said.

Tancredo will register his new party affiliation with the Colorado Secretary of State and the party will form a vacancy committee to put him on the ballot by the end of the week, a spokeswoman said.

Both Scott McInnis and Dan Maes refused to go along and said they will continue campaigning for the Republican nomination.

Tancredo said he believes the two GOP candidates have no chance of winning the general election against Hickenlooper.

The Colorado Statesman reported that current American Constitution Party gubernatorial candidate Ben Goss is defending Tancredo’s party shift as longtime coming.

“A lot of people are trying to cast Tancredo as an opportunist (and) that’s wrong. He didn’t just jump into this -- it’s a culmination of two years of talks with Tom,” said Goss.

Dick Wadhams, head of the state’s Republican Party, also said Tancredo's running would split the Republican vote in the general election, giving Hickenlooper the win.

"There's no doubt, Tom Tancredo running on a third party ticket will dramatically, diminish, if not, make impossible our abiilty to defeat John Hickenlooper," said Wadhams in an interview with 7NEWS.

Tancredo said Wadhams criticized McInnis and Dan Maes in private, which Wadhams denied.

In an interview with the two men on KHOW radio, Wadhams said he noted both candidates both had problems, but claims he didn't criticize them.

Tancredo's anticipated run for governor had a stumble before he even declared himself a candidate.

Twenty-one state Tea Party groups issued an open letter to Tancredo Sunday warning that his third-party bid would be a "disaster, assuring victory" for Denver Mayor John Hickenlooper, the Democratic candidate. The groups accused the former congressman of “subverting the process and our will.”

Beyond the Governor's race, Wadhams feels Tancredo could be such a distraction, Republicans could lose local races for the House and Senate.

"It has the impact to change those races," said Wadhams.

The groups said Tancredo's "High Noon ultimatum … completely contradicts" his own advice in a Dec. 21 open letter to Tea Party supporters that third-party campaigns have historically backfired.

"Leaving the party is not the answer," Tancredo wrote at the time. "Throughout our nation’s history, third parties have never succeeded in taking power and running the government… Often, they succeeded only in electing the more liberal candidate."

The Tea Party groups had urged Tancredo to withdraw his ultimatum and work within the Republic Party.

"We trusted and listened to you …but now you do not trust the Republican voters of Colorado to thoughtfully and logically evaluate the choices before us," the Tea Party backers wrote. "You want to impose your personal choice and will over the will of the people. You are subverting the process and our will. This is the opposite of the liberty movement and what we are about."

In the wake of the Tancredo ultimatum, the group's said an unscientific poll of members found 66 percent of the 754 respondents would not vote for Tancredo for governor.

"This does not foretell a conservative victory, but rather an impending disaster, assuring victory for Mayor Hickenlooper and the liberal agenda in Colorado for at least four more years," the groups said.

"I think I can be a credible candidate," said Tancredo. "I will run as hard as I possibly can and I am going to the offer the people in this state a choice."

Maes, discussing Tancredo's decision to run, said, "I think it's a bit arrogant of Tom ... It's high noon, and I'm still here."

Shortly after noon, McInnis issued a statement that said:

"This election is about job creation, a stronger business climate, an end to unconstitutional tax increases and a commitment to reduce the size and scope of state government. We have elections to battle out competing visions for Colorado's future, and our fellow citizens are voting in the primary today as they have been for the past week.

"Those looking for a deadline should focus on the only real deadline: August 10 at 7 p.m. This is when the polls close, the people have voted and their votes are counted. That's the way the system works in a free society.

"Colorado Republicans will speak with their votes on that day, and I will abide by their decision."

During a decade representing a suburban Denver district in Congress, Tancredo hasn't hesitated to publicly spar with both Democrats and his fellow Republicans.

Tancredo founded the Congressional Immigration Reform Caucus and achieved national recognition with aggressive, biting rhetoric against what he called out-of-control immigration and bilingual education.

He once said Miami was like a Third World country because of its growing non-English-speaking population.

His poorly funded, long-shot run for president ended in 2007. He didn't seek re-election to Congress in 2008.