The Club for Growth has successfully remade the Republican Party by helping purge it of its remaining moderate vestiges. Yet the fact that so many of its candidates have ultimately lost lends weight to the argument that the club is doing more electoral harm than good to the GOP.

[IMGCAP(1)]This view will be tested in Nevada, where fringe conservative Sharron Angle rode club support to win the recent Senate primary, upsetting an establishment choice and assuming the right to take on Republicans’ No. 1 target, Senate Majority Leader Harry Reid (D). With Reid’s weakness, it is a race Republicans should easily take, but Angle has turned the contest into a tossup. It is perhaps the biggest race of the group’s existence, as an Angle defeat would be a devastating indictment of the Club for Growth’s credibility.

Despite its relatively small size, the Club for Growth is able to exercise enormous control over the GOP because of its significant financial resources. Built around its support of lower taxes, ending the inheritance tax and expanding free trade, the club jumps into Congressional races to take on candidates and incumbents it labels as RINOs — Republicans in name only — with sufficiently conservative Republicans.

Of course, there are many forces behind the GOP’s shift, particularly the mass retirements and defeats of the last Northeastern Republican Congressmen. But the club’s work in expelling moderates has been one of the critical drivers, changing the anatomical structure and directional tone of the GOP. In actually electing its choices, the club’s record is decidedly mixed, as its nominees have been repeatedly rejected.

In one of the club’s groundbreaking forays, it went after moderate Pennsylvania Sen. Arlen Specter in 2004, backing then-Rep. Pat Toomey in a Republican primary that Specter won by less than 2 points. Toomey, who subsequently became Club for Growth president, is seeking the seat again this year.

In 2006, the club tried to oust Rhode Island Sen. Lincoln Chafee in a Republican primary; Chafee survived but was bruised enough that he lost a tight general election in a blue state that Republicans were very lucky to hold in the first place.

Club-backed conservatives cost the GOP two seats in 2008. In Michigan, the club helped Tim Walberg beat Rep. Joe Schwarz in the 2006 Republican primary, but Walberg was ousted just two years later in the general election in part because he was too conservative for his district. Similarly, the club toppled popular Maryland centrist Wayne Gilchrest with a right-wing state Senator in the 2008 GOP primary, allowing Democrats to steal the red seat.

Which brings us to Nevada, the club’s biggest test of all. Reid is one of the nation’s most powerful Democrats, and importantly, his longtime shaky standing at home appears to have finally caught up with him. In other words, Reid should be politically extinct, with polls saying as much for months, and Republicans have absolutely no excuse for him winning.

Enter Angle, who embodies the prototypical club nominee. A caustic conservative, she supports ending Social Security and closing the Department of Education. Perhaps more tellingly, she is an established loser. Running for an open conservative House seat in 2006, Angle lost the primary — ironically, with $1 million of club support — after which she alleged fraud and demanded a new election. Two years later, she was defeated in a quixotic primary run against the state Senate president.

Repeatedly rejected by some of Nevada’s most conservative voters in smaller matchups, Angle is a poor choice for a statewide run. With Nevada unemployment rates persistently high, almost any Republican should win this race. But Reid has almost $10 million on hand while Angle’s campaign is almost broke; furthermore, Nevada remains a swing state and one that President Barack Obama carried by 12 points. Angle’s positions are a better fit in Idaho or Utah.

To be sure, Angle’s Republican primary victory cannot be solely attributed to the Club for Growth’s efforts. Angle rose with the support of tea party groups and the collapse of the frontrunner amid a series of inexplicable miscues. But it was the club’s infusion of more than $400,000 worth of television commercials in the final weeks that changed the trajectory of the race and propelled Angle into the lead. As one of Angle’s opponents noted, the club ads seemed to be on Fox News “about every 10 seconds.”

The club’s intervention thus paves the way for the most important challenge in its history. In Angle, it has a true-blue conservative in a contest against a deeply unpopular Senator in a fiercely anti-incumbent year. If elected, Angle would become the Club for Growth’s most high-profile triumph and would enable it to argue that it can indeed have its cake and eat it too by bagging a swing state Senate seat with a staunch conservative.

But if Angle loses and Reid’s dour mug returns to Washington, it will be a cutting rejection of the Club for Growth’s very existence. It will demonstrate in stark terms that the club’s one-size-fits-all approach to elections is long-term electoral suicide for the Republican Party. With these stakes and Angle’s precarious financial position, expect the club to flood Nevada with propaganda from now until November.

Given the club’s influence and the unswerving beliefs of its patrons, one defeat will not change its core mission to purify the GOP, even if it should.

But in Nevada this year, the Club for Growth is going to have to put up or shut up.

Mark Greenbaum is a Washington, D.C., writer.