Fresh off their first victory over a Republican incumbent, GOP conservatives seeking party purity on taxes and spending are focused on ousting moderate Republican Sen. Lincoln Chafee of Rhode Island.

The Club for Growth and its 36,000 members spent around $1 million to help challenger Tim Walberg unseat first-term Rep. Joe Schwarz in Michigan's Republican primary on Tuesday. The win came despite Schwarz's support from President Bush and the National Rifle Association.

Since its inception in 1999, the group has spent millions to help dozens of conservative Republicans win seats in Congress — often at the expense of more moderate party members. The Club's president, former Rep. Pat Toomey, nearly defeated Pennsylvania Sen. Arlen Specter in 2004.

This year, the group's top priority is defeating Chafee, who angered many Republicans by voting against President Bush's tax cuts and then casting a write-in vote for the president's father in the last election. The Club has helped Cranston, R.I., Mayor Stephen Laffey raise hundreds of thousands of dollars to unseat Chafee, and polls show the two Republicans running even a month before the Sept. 12 primary.

The prospect of a Laffey win worries national Republicans, who consider Chafee the party's best bet for holding the seat in a heavily Democratic state. Polls show Laffey trailing far behind the leading Democratic candidate, former Attorney General Sheldon Whitehouse.

The Club's Web site says that's fine: "It wouldn't be much of a loss if a new Democrat senator were elected, as he would vote much the same as Chafee does now."

Republicans who support the Club say its refusal to compromise its ideology gives it credibility.

"They're not about getting more Republicans elected, they're about getting real Republicans elected," said Jerry Stacy, spokesman for Sharron Angle, a Club-endorsed House candidate in Nevada.

But Chafee is a Republican who votes with his party most of the time. His father, the late John Chafee, is revered in Rhode Island as a World War II hero who served three terms as governor and more than 20 years in the Senate. Like his father, the younger Chafee is a fiscal conservative and environmentalist.

Moderate Republicans criticize the Club for targeting incumbents like Chafee instead of going after Democrats.

"I refer to the Club for Growth as the enemy within," said Rep. Sherwood Boehlert, R-N.Y., whom the Club opposed in GOP primaries in 2002 and 2004.

Economic conservatives founded the Club to encourage the federal government to adopt "pro-growth economic policies." That includes making the Bush tax cuts permanent, repealing the estate tax, cutting government spending and expanding free trade.

One Club tactic is providing campaign cash to candidates who espouse a free market philosophy. It raised $22 million for issue advocacy, candidates and operations in the last election cycle.

This year, the club and its 36,000 members were responsible for $1.1 million of the estimated $3 million spent on Michigan's Republican primary. The group opposed Schwarz even though he — like Chafee — was endorsed by Bush. Also like Chafee, Schwarz has criticized the war in Iraq, supports abortion rights and favors stem-cell research.

Steve May, a former Arizona lawmaker who served briefly as a Club chapter president before being pushed out, said the organization throws conservative challengers up against moderate incumbents to scare them to the right.

"For the Club for Growth, it's all about the money, but you have to pass the social litmus test," May said.

May said he was ousted in 2003 because he was gay. Toomey said it was because May voted for a tax increase.

Toomey insisted the organization doesn't make choices based on party or positions on social issues. He noted that it endorsed its first Democrat this year — conservative Texas Rep. Henry Cuellar.

Many Club members hope Laffey, the Club's candidate in Rhode Island, will give them another win. They have contributed more money to his campaign than any other this election, well over $600,000, Toomey said. At the same time, the Club's political action committee has spent almost a quarter of a million dollars on anti-Chafee ads.

"Helping Steve Laffey win this race is as high a priority as we have for this cycle," Toomey said.

Sarah Chamberlain Resnick, executive director of the Main Street Republican Partnership, which is backing Chafee, said the Club's efforts will only help Democrats gain more seats in Congress.

"(House Minority Leader) Nancy Pelosi should make sure that Pat Toomey is on her Christmas card list," Resnick said after Schwarz's defeat.