The Club for Growth cemented its role as the preeminent third-party group in Republican primaries on Tuesday, guiding Richard Mourdock to a stunning 22-point win over six-term Sen. Richard Lugar (R-Ind.).

By the end of the Indiana campaign, the Club and its affiliated political action committee, Club for Growth Action, dumped nearly $2 million into ads against Lugar, far exceeding investments by groups like the National Rifle Association ($600,000), Citizens United ($96,000) and spending more on ads than both Lugar ($1.6 million) and Mourdock ($700,000).

View Photo Gallery: A look at the career of Republican Sen. Richard Lugar of Indiana.

It’s just more of the same from a group that has successfully picked its battles over the years and toppled a series of more moderate Republican incumbents and establishment candidates, with very few big losses along the way.

But while the win might have been the Club’s biggest upset to date, the real test may lie ahead.

The Club has backed candidates in four Senate primaries in the coming months, and all but one is an underdog. In addition, it appears likely the Club’s hand-picked candidate will finish third in Nebraska next week.

But first, the Club’s record:

The Club for Growth’s strategy has long been to pick its spots, investing more money and time in fewer races in order to have the maximum impact possible. Generally, it will get involved in a couple high-profile primaries and try to guide the underdog to victory.

And much more often than not, it has.

In 2010, the Club helped defeat incumbent Sen. Robert Bennett (R-Utah) for renomination and nudged Sen. Arlen Specter and Florida governor Charlie Crist out of the Republican Party after backing their opponents. It also helped tea party favorite Sharron Angle win a Senate primary in Nevada. Its candidates lost just two primaries — both of them in the House — out of more than a dozen.

The Club also backed Rep. Steve Pearce in his win over Rep. Heather Wilson in the 2008 New Mexico GOP Senate primary and helped defeat longtime moderate congressmen Wayne Gilchrest (R-Md.) in 2008 and Joe Schwarz (R-Mich.) in 2006.

It’s first big entree into GOP primaries was in 2004, when it nearly guided now-Sen. Pat Toomey to a primary upset over Specter and helped now-Sen. Tom Coburn (R-Okla.) defeat a heavily favored primary opponent.

Toomey’s loss aside, there have been remarkably few big-time primary defeats, the most notable being the Club’s failed attempt to beat then-Sen. Lincoln Chafee (R-R.I.) in a 2006 primary. Indeed, when the Club gets involved in big-time races, it usually wins — at least in the primary.

Updated at 11:03 a.m.: A reader notes that the Club has backed losing candidates in a few House primaries already this year, failing to beat Rep. Tim Murphy (R-Pa.) and losing GOP contests to face Rep. Jim Matheson (D-Utah) and for retiring Rep. Dan Burton’s (R-Ind.) seat.

That win streak will be tested in the weeks ahead, though, as Club-backed candidates face tough odds in Senate primaries in Nebraska and Texas.

In Nebraska next week, Club-backed state Treasurer Don Stenberg has slipped to third in the most recent poll (though Club backers note their campaign was mostly anti-Jon Bruning, and he could still fall to state senator Deb Fischer, who announced the backing of Sarah Palin on Wednesday).

Then, on May 29, Club-backed former Texas solicitor general Ted Cruz will be looking to earn a berth in the runoff against Lt. Gov. David Dewhurst. Recent polling shows Dewhurst flirting with the 50 percent threshold he needs to avoid the runoff, but even if it goes to a two-man contest, Cruz will be an underdog.

The Club is also backing former congressman Mark Neumann in a tight Senate primary battle in Wisconsin with former governor Tommy Thompson and businessman Eric Hovde, and Rep. Jeff Flake against an insurgent self-funding businessman in Arizona’s open Senate contest.

Of the four races, the Club is backing the favorite in only one (Flake).

“Our main concern isn’t our record,” said Club president Chris Chocola. “We want to win, no question, but we’re not overly concerned with our record. We take risks, that’s what we do. We almost never endorse the favorite or the establishment candidate.”

The Club has gotten involved in more high-profile primary races this year than it ever has — a byproduct of both the importance of the battle for the Senate and the increasing money it can raise in the super PAC era. It’s investment in Mourdock was one of its largest in any primary to date.

There will be plenty of money spent in the months ahead, too.

Texas, in particular, is going to be very expensive if it goes to a runoff. The Club has already helped Cruz raise $1 million and announced Wednesday that it is plugging $1 million into an ad campaign against Dewhurst, who will never suffer for funds by virtue of his extensive self-funding capabilities.

It’s very much an uphill battle for the Club, but the group is off to a good start.