When brewery scion Peter H. Coors jumped into the race for Colorado's open U.S. Senate seat this spring, he knew that his maiden political venture would involve harsh criticism and fiery rhetoric. What he did not know was that much of the fire aimed his way would come from the corporation he ran until three months ago.

The heir to the Coors Brewing fortune is fighting an increasingly nasty campaign against a scrappy but underfunded former House member, Bob Schaffer, for the Republican Senate nomination. But the Coors vs. Schaffer contest has often taken a back seat to a different confrontation: Coors vs. Coors.

Fearing a revival of activist boycotts that used to hamper its sales, Coors Brewing Co. has attacked its former chairman's political positions. Candidate Coors, 57, meanwhile, has struggled mightily to distance himself from the lusty advertising and pro-gay social positions of the company that bears his name.

"It's clear I've become a lightning rod," Coors says in sadder-but-wiser tones. "If people don't agree with where I am, they'll take it out on the company. And if they don't like what the company is doing, they go after me."

Even if he prevails in the Aug. 10 primary, however, Coors looks like an underdog in the fall campaign. State Attorney General Ken Salazar, a popular figure with statewide appeal, seems likely to win the Democratic Senate nomination. Polls show Salazar leading both Republican hopefuls in head-to-head matchups.

All of which reflects the stunning turnabout of Colorado's 2004 Senate race. A seat that was universally rated as a "safe Republican hold" at the beginning of this year has suddenly become a "likely Democratic gain" in most pundits' predictions.

The Republican incumbent, Sen. Ben Nighthorse Campbell, seemed unbeatable until March, when he got snarled in a federal investigation of alleged financial kickbacks in his office. Citing health problems, Campbell abruptly dropped out of the race. Democratic leaders quickly settled on Salazar as their consensus choice.

The attorney general faces a challenge from newcomer Mike Miles in the Democratic primary, but polls suggest Salazar will take the nomination easily. The state's Republicans, in contrast, went through an embarrassing month as all their best-known prospects declined to run.

Eventually, Schaffer, 42, an energetic man with close ties to conservative organizations such as Focus on the Family, announced his candidacy. Party leaders were tepid. Republican Gov. Bill Owens and others began looking for a different candidate, and found one in the corner office here at the nation's third-largest brewery.

In a state where sipping a Coors Light in the stands at Coors Field is a standard summer pastime, Peter Coors had almost-total name recognition, broad business connections and millions of dollars to spend on a Senate campaign. And yet Coors's drive toward the GOP nomination has been considerably bumpier than expected.

The beer baron has come across as ill-informed and unprepared on national issues. "Coors light on facts," declared a Denver Post headline after one campaign appearance.

In his TV ads, Coors calls for more federal tax cuts and a balanced federal budget. Asked how he would reconcile those two goals, he replied: "That's probably a fair question, but I just don't have an answer for you."

In a debate, the wily Schaffer demanded to know whether Coors agreed with Paul Martin on U.S.-Canadian trade. Coors fell right into the trap. "I'm not sure I know who Paul Martin is," he said warily. Schaffer pounced: "A U.S. senator needs to know who the prime minister of Canada is."

Schaffer's backers have also criticized a campaign ad in which Coors boasts that he moved up from floor sweeper to chairman of his company -- without mentioning that he inherited the top job from his father. Even worse, the campaign is caught in an ongoing squeeze involving the candidate, his family firm and social conservatives who are critical of the company.

Although he hesitated at first about backing the constitutional amendment banning gay marriage, Coors eventually endorsed the proposal -- a requisite stance in a GOP primary here. In response, Coors Brewing virtually accused Peter Coors of endorsing discrimination.

"We do not support discrimination against the gay-lesbian-bisexual-transgender community, via legislation or otherwise," the company said. Coors, the brewery, is now buying ads in gay newspapers to emphasize its disagreements with Coors, the candidate.

At the same time, social conservatives backing Schaffer are running TV ads that denounce candidate Coors because of the "degrading and nearly pornographic" ads that his company uses to sell beer to young men. The same ads argue that Coors's family firm has embraced "the homosexual agenda" with its financial support of gay organizations.

Criticized early in the campaign for his failure to take any stand on the war in Iraq, Coors eventually declared that he agrees with his opponent on all major issues. "It's the most unimaginative campaign message I've ever seen," Schaffer says. "So we looked for something where he had taken a position, and finally we found it."

As a beer salesman, Coors has regularly argued for lowering the drinking age. So, now, Schaffer is highlighting that stance. "The drinking age wouldn't normally be an issue in a Senate campaign, but it's what we've got," he says.

Internal polls in both campaigns show a tight primary race that could depend on voter turnout. If only dedicated GOP activists vote, Schaffer's conservative connections could decide the race. In a broader turnout, though, Coors's name recognition and constant TV ads might be decisive.

But if Coors gets to the general election, he will still have the family firm looming over his shoulder. "It's not a bad deal," says Denver Democratic consultant Terry Snyder. "As long as Coors Brewing is beating up on Pete Coors, the Democrat doesn't have to."

Brewery heir Peter H. Coors, left, and former House member Bob Schaffer are seeking the Republican nomination for the Senate race in Colorado.