On the issues, it's been hard to tell the difference between the two Republican candidates vying for a shot at Colorado's open Senate seat.

Peter Coors (searchand Bob Schaffer (searchboth support President Bush's stance on Iraq, oppose abortion under any circumstances and think school vouchers are a good idea.

They're also in agreement over a constitutional ban on gay marriage, although Coors had said earlier that he wasn't sure it was necessary.

But the similarities are likely to fade after the state GOP convention this weekend, political experts said. At that point, Coors, the brewery heir, will probably begin offering himself as a moderate alternative to Schaffer, a conservative former congressman.

And if Coors wins the primary, experts say another reinvention is likely against the Democratic nominee, either educator Mike Miles (search) or Attorney General Ken Salazar (search).

"It's the classic problem in American politics. He has to appeal to his base, then flip to the center to get the moderate vote in the primary, then shift again for the general election," said John Straayer, a political science professor at Colorado State University.

The race has drawn national attention because a seat once considered a Republican lock was put into play with the retirement of GOP Sen. Ben Nighthorse Campbell (search). In the Senate, Republicans hold a slim 51-48 majority with one Democratic-leaning independent.

Observers say Coors has been forced to endear himself to the party's right wing to win a spot on the Aug. 10 primary ballot during Saturday's convention.

That became clear after the Coors Brewing Co. distanced itself from Coors the candidate, its former chairman, by saying his support for a constitutional ban on gay marriage does not reflect the company's position.

"We do not support discrimination against the gay-lesbian-bisexual-transgender community, via legislation or otherwise," said CEO Leo Kiely.

Coors Brewing was once boycotted by gays because it required job applicants to take a polygraph test that included questions about sexual beliefs. The company is now considered a model for recruiting gay workers and offers same-sex partner benefits — something for which candidate Coors has taken credit.

Cinamon Watson, his campaign spokeswoman, said the issue changed when states began issuing marriage licenses to gays earlier this year.

"At some point you have to separate Peter Coors from the company and listen to how Peter Coors defines himself as a candidate," she said.

Schaffer and Coors are both expected to win support from at least 30 percent of the GOP delegates, which will get them on the primary ballot. Coors has enough money to hire canvassers to gather signatures and make the ballot through petitions but rejected that route.

"He feels like activists are the backbone of the party and he felt he needed to respect the process and go through the convention," Watson said.

Schaffer's campaign manager, Pat Fiske, welcomed the decision, saying it will make it easier to restore party unity after the primary.

One current difference between the two candidates is financing. Despite his late start, Coors has raised more than $1 million for his campaign from outside donations. Schaffer has raised $400,000.

"We never felt we would have as much money as Coors would have," Fiske said. "We don't need it. We have a much larger grass-roots, volunteer organization."

The two candidates also disagree on tax policies. For one thing, Schaffer backs the Taxpayer's Bill of Rights, a voter-approved measure that limits the amount of taxes the state can spend without taxpayer approval. Coors says the amendment shifted the tax burden to corporations, which ultimately hurts everyone in Colorado.

Both candidates will target 3,478 party activists, including Teller County GOP chairman Paul Crowson, who said he has not decided on a candidate.

"We want them to woo us and convince us. They'd better," he said.