Sen. Ben Nighthorse Campbell’s (R-Colo.) re-election battle, which seemed like a snoozer just a couple of weeks ago, gets more interesting by the day — and has sparked a new round of speculation that the two-term Senator may ultimately forgo the race.

Once-despondent Democrats are clearly energized by philanthropist Rutt Bridges (D), who officially entered the race this weekend and said in an interview Monday that he is willing to spend “whatever it takes to ensure a fair fight” in his Senate bid.

Campbell, who appeared invulnerable only a few weeks ago, has been rocked by a recent controversy surrounding his staff and by renewed questions about his health.

“The game is afoot, the field is set,” said Chris Gates, chairman of the Colorado Democratic Party. “I’m glad to finally know that this is it.”

While stopping short of taking sides in the Aug. 10 Democratic primary battle between Bridges and educator Mike Miles, party leaders are heaping praise on Bridges, a businessman who runs a Denver-based think tank and has been an integral part of Colorado political and civic life.

“Rutt Bridges is the real deal and we are thrilled he has decided to make this race,” said Democratic Senatorial Campaign Committee Chairman Jon Corzine (N.J.).

Miles, who has been in the race for two years, is running a low-budget, grassroots campaign and had $42,000 in the bank at the beginning of the year.

But behind-the-scenes maneuvering — and whispering — suggests that the field is not necessarily set yet, and that Campbell would be the catalyst in any shakeup.

Following a week of bad headlines late last month surrounding the resignation of Campbell’s longtime chief of staff, Ginnie Kontnik, and allegations that she demanded a kickback from an underling with the Senator’s tacit approval, some political observers wonder whether Campbell will have the stomach to continue as the Senate Ethics Committee and possibly the Justice Department investigate.

That has sparked wild speculation that the Senate contest could ultimately come down to a battle between Rep. Mark Udall (D-Colo.) and Gov. Bill Owens (R). That scenario assumes that Campbell will eventually drop out of the race — something his campaign operatives vehemently deny — and that Udall will reconsider his decision to stay in the House.

“There’s always all sorts of rumors about [Republicans] switching Campbell out” in favor of Owens, said one Democratic state official in Colorado, speaking on the condition of anonymity.

Rumors of a sudden Campbell departure from the Senate race have been swirling around the state all cycle — some of them generated by wishful-thinking Democrats. But Republicans have privately conceded that Campbell is unpredictable enough to pull out at a moment’s notice.

The speculation intensified after Campbell reluctantly revealed last fall that he was undergoing treatment for prostate cancer, and picked up again after Campbell checked himself into George Washington University Hospital with chest pains last week. Doctors said the 70-year-old Senator had severe heartburn.

After a weekend of rest, Campbell returned to work Monday and is “just fine,” his Senate spokesman Kate Dando said.

Meanwhile, Campbell’s Denver-based campaign consultant, Sean Tonner, said the Senator is more fired up than ever about running now that a wealthy Democrat is in the race.

“The odds of Ben Campbell getting out are right up there with the Cubs or Red Sox winning the World Series this fall,” Tonner said. “It ain’t going to happen.”

But many Colorado political operatives believe that Owens, who cannot seek a third term in 2006 and has barely masked his national ambitions, would jump at the chance of getting into the Senate race if Campbell got out.

One political insider in Denver suggested that Owens’ announcement last week that he was putting state Attorney General Ken Salazar (D) in charge of the criminal investigation of a University of Colorado football team scandal — a move that infuriated many statehouse Republicans — was a sign that Owens is moving to the center in anticipation of a possible statewide run.

Owens does not want to be seen as pushing Campbell out the door, and probably can’t as a practical matter: His political team, including Tonner, is now working for Campbell, who hasn’t had many close political confidantes in Colorado since he switched parties in 1995.

Tonner blamed the rumors about Owens and Campbell on “Democrat operatives.”

Rep. Scott McInnis (R-Colo.), who has already announced his retirement, is also mentioned as a possible Senate candidate if Campbell bows out. There has been renewed speculation in the past few days, meanwhile, that McInnis could step down before the end of the 108th Congress to take a job in the private sector.

Blair Jones, McInnis’ spokesman, said his boss is focusing only on his Congressional job.

Dan Allen, communications director for the National Republican Senatorial Committee, said Senate Republicans are proceeding under the assumption that Campbell, who started the year with $1.3 million in the bank, will be their nominee.

“Senator Campbell is well-positioned for re-election,” Allen said. “He’s worked hard over the past year raising money and kicking off his campaign.”

If Campbell were to get out soon for some reason, many Democrats believe Udall would re-examine his decision not to run for Senate this year. After a year of flirting with the race, Udall announced in late December that he would seek a fourth term in the House rather than challenge Campbell. Implicit in that statement was that if Campbell departed the scene, Udall, who had $539,000 in the bank at the end of 2003, might take another look.

“It’s a hypothetical, and it’s kind of hard to respond to a hypothetical,” said Lawrence Pacheco, Udall’s spokesman. “The Congressman has said he will not challenge Ben Campbell, and as far as we know, Senator Campbell is a candidate.”

But one leading Colorado Democrat said that as the negative headlines about Campbell have piled up, there is talk that “maybe [Udall] regrets his decision.”

Unlike some Colorado and Washington Democrats, Udall does not appear ready to endorse Bridges soon. Bridges and the Congressman have spoken recently, but neither side would reveal what was said. Bridges said he is expecting “a lot of endorsements” from leading Colorado Democrats “very soon.”

Pacheco said Udall “feels that he needs to speak to other [Senate] candidates before talking about an endorsement.”

Several Democrats said they could not imagine Udall and Bridges squaring off in a primary, and Gates, the Colorado party chairman, said it is late for the Congressman to get into the Senate race.

Assuming Udall does not run, most Democratic leaders appear comfortable with Bridges, a moderate Democrat who is best known in Colorado for sponsoring the measure that created a “do not call list” for consumers who do not want telemarketers to call them.

After making his announcement at the Colorado Historical Society museum in Denver on Sunday, Bridges gave speeches in Denver Monday and is scheduled to travel to Manitou Springs and Colorado Springs this morning. Bridges is slowly assembling a campaign team. So far his advisers include Sue Bachar, a former strategist with the Dutko Group in Washington who now lives in Colorado; Tyler Chaffee, a Democratic operative who worked for former Sen. Bill Bradley’s (D-N.J.) presidential campaign in 2000; and Jeff Bridges, the candidate’s son, a veteran of Colorado Democratic campaigns.

“The first 24 hours [as a candidate] have been pretty surreal,” Bridges said Monday. “I think it will be an interesting journey.”