Just weeks after entering the race with a storm of confidence and enthusiasm, former Rep. Scott McInnis (R) announced late Wednesday he will not be a candidate next year for the Colorado Senate seat being vacated by retiring Sen. Wayne Allard (R).

“My decision is based on doing what is right for Colorado, and ultimately what is right for my family,” McInnis said in a statement. “I will remain actively involved, just not on the ballot.”

McInnis’ announcement could represent a blow to GOP prospects of holding Allard’s seat. McInnis, a maverick Republican during his dozen years in Congress, was seen as capable of drawing independent and moderate voters in a statewide general election.

All eyes are now likely to turn to former Rep. Bob Schaffer (R), who lost a close primary contest for Senate to beer magnate Pete Coors (R) in 2004 and has retained a large measure of goodwill among Republican activists both for his previous service in Congress and the way he conducted himself during that campaign.

Schaffer is more closely identified with the conservative wing of the state GOP than McInnis was, and was endorsed earlier this week by former Sen. Bill Armstrong (R), the godfather of Colorado conservatives.

Schaffer said in a telephone interview Wednesday evening that he is still considering running next year. But he declined to elaborate on his thought process beyond confirming his previous statements that he believes Republicans must unite behind a consensus candidate if they are to defeat the Democratic nominee, who, at this point, looks to be Rep. Mark Udall (D).

“The big question is whether a centrist reform-oriented candidate — which would be most Republicans, but certainly me — is able to capture the majority of votes in 2008,” Schaffer, an executive with Aspect Energy, said. “That’s what I’m evaluating, whether a centrist reformer can win.”

Schaffer matter-of-factly noted that Democrats have had a spate of success statewide in recent years, winning an open Senate seat, both chambers of the state Legislature in 2004 and capturing the governorship last year. The Democrats also have picked up a House seat in each of the previous two election cycles.

Knowledgeable Colorado Republicans say McInnis’ exit also elevates the stock of state Attorney General John Suthers (R), who has won statewide and serves in the same position that propelled now-Sen. Ken Salazar (D) to Washington, D.C., in 2004. Suthers said in the past week that he is considering a Senate run.

One Republican operative based in Colorado predicted that McInnis’ announcement would elevate both Schaffer’s and Suther’s interest in the race. While Schaffer is considered a darling of conservative Republicans, this GOP insider said the former Congressman appealed to moderates and independents when he represented the 4th district.

“I’d think at this point, they would consider the race more seriously,” this operative said. “Both would be very formidable statewide candidates.”

McInnis launched his exploratory committee toward the end of February, after signaling that he wanted to run as soon as the Allard retirement rumors began percolating in early December.

With almost $1 million sitting in his old 3rd district House campaign account, McInnis was seen by political observers as an early frontrunner and a formidable candidate — a characterization he promoted at every turn.

Since the beginning of the year, McInnis was working to assemble a team of advisers, while courting Colorado’s major Republican donors. In his effort to avoid a primary, he traveled up and down the state trying to secure the support of both the moderate and conservative wings of the Centennial State GOP.

But he was coming under attacks from Republicans who were unhappy with some of his moderate positions, and from Democrats for his work as a Denver-based lobbyist after retiring from Congress. McInnis also was criticized for employing his wife on his House campaigns.

A spokeswoman for the National Republican Senatorial Committee didn’t have much of a reaction to McInnis’ announcement beyond wishing him well. But the Democratic Senatorial Campaign Committee took the opportunity to gloat.

“Scott McInnis’ withdrawal from the race is a major blow to Republican efforts to hold onto a Senate seat in Colorado, and another sign that the political environment continues to be extremely poor for the GOP,” DSCC spokesman Matthew Miller said in a statement.