It also comes as more conservative members of the House and Senate continue to concern Republican leaders as they seek cohesion in their party.
“The Club for Growth is homogenizing the Republican Party," Snowe said in an interview with Post Politics. “The Republican Party is going to have to mature.”
The head of the Main Street organization, former congressman Steven LaTourette (R-Ohio), said it has already raised $2.5 million toward its goal and that he and Snowe will barnstorm the country together to raise the rest. The group will make expenditures from both its nonprofit issue advocacy arm and its super PAC, allowing donors to contribute to either (nonprofit donors do not need to be disclosed).
But even LaTourette acknowledged that the money and enthusiasm in many of these primaries is with the Club and its allies, which include Heritage Action and the Senate Conservatives Fund.
"Eight million dollars isn’t going to change the country," LaTourette said. "This is sort of a baby step that we’re beginning with the try to level the playing field."
Tensions between Main Street -- former known as the Republican Main Street Partnership -- and the Club for Growth festered over the last week following the Club's endorsement of Rep. Mike Simpson's (R-Idaho) primary challenger, attorney Bryan Smith.
Simpson, like LaTourette, is a GOP moderate and ally of House Speaker John Boehner (R-Ohio). Boehner has in recent months struggled to deal with an unruly Republican conference -- many members of which were elected with the help of the tea party and groups like the Club for Growth.
LaTourette said GOP primary voters in a conservative district like Simpson's have a right to nominate someone else, but he said that groups like the Club for Growth have played an outsized role in such races, leaving moderates with little ammunition to fight back.
He also said the Club has crafted a fraudulent reputation as a grassroots organization.
"If this was some broad-based populist movement, I get that," LaTourette said. "But if you peel back the onion, the Club for Growth is really five or six guys that have a lot of money and bigfoot the Republican primaries."
The Club on Tuesday hit back at LaTourette, pointing out the amount of money Simpson has raised from another small group of influential players -- political action committees.
"It’s a joke for Mike Simpson and his allies to cry foul on outside groups supporting his conservative challenger; 64 percent of Mike Simpson’s campaign contributions have come from Washington PACs, not the people of Idaho,” said Club for Growth spokesman Barney Keller. “Mike Simpson is the same congressman who rakes in millions from special interests that he regulates, all while voting to raise his own pay nine times and spending thousands on lavish events at Washington D.C. social clubs.”
LaTourette said his group will seek to play in a limited number of races where it can have a bigger influence. He mentioned potential Club for Growth targets including Senate candidate Rep. Shelley Moore Capito (R-W.Va.) -- who has been involved with the group -- and Reps. Aaron Schock (R-Ill.) and Susan Brooks (R-Ind.), along with Reps. Rodney Davis (R-Ill.) and David Joyce (R-Ohio). Joyce holds the seat LaTourette retired from last year.
LaTourette acknowledged his group has to walk a fine line in some of these races, as its involvement could lead candidates to be tagged as RINOs -- Republicans In Name Only. Another recently launched group seeking more electable GOP candidates, Karl Rove's Conservative Victory Project, has dealt with similar accusations that it is anti-conservative.
"Some members might have the opinion, 'Gosh, if these guys get involved I’ll be known as a friend of the RINOs,'" LaTourette said. "That’s something we’ll have to engage on a race-by-race basis."
The Club has launched a Web site at PrimaryMyCongressman.com to identify which members its supporters think should be unseated. Simpson was its first announced target.
Main Street, meanwhile, is launching its own Web site at ClubforDemocraticGrowth.com. The Club's critics have often used the nickname for the group, noting that some of its nominees wound up losing winnable races or that more moderate candidates emerged bruised and battered from primaries against Club-backed candidates.
The most cited examples include 2010 Nevada GOP Senate nominee Sharron Angle and 2012 Indiana Senate nominee Richard Mourdock, who both lost after beating establishment candidates. GOP establishment types also blame the Club for hurting once-popular former Wisconsin governor Tommy Thompson in his primary last year. Thompson narrowly won his party's nomination but eventually lost to Rep. Tammy Baldwin (D) in the general election.
“It’s a fact that the Club for Growth supported those candidates when almost no one else did,” Club President Chris Chocola said in a December interview with Politico. “People want to throw out Angle and Mourdock; that’s fine. We supported those candidates. And they lost.”
GOP leaders have also struggled with Club-backed Republicans once they've joined Congress, including Reps. Justin Amash (R-Mich.), Tim Huelskamp (R-Kan.) and David Schweikert (R-Ariz.). These members often vote against leaders on big-ticket items, taking the same positions urged by groups like the Club and Heritage Action.
The Club notes that the vast majority of its candidates performed just fine in the general election and that it helped Sens. Pat Toomey (R-Pa.), Marco Rubio (R-Fla.) and Ted Cruz (R-Texas) win their seats in recent years.
LaTourette said Republicans need to focus on expanding their appeal rather than closing ranks around conservatives and having litmus tests for their congressional incumbents.
"You can't wake up and go into an election and say, 'Okay, let's see who's voting for us? Angry white guys in their 50s are voting for us. Who's not voting for us? African-Americans, Hispanics, gays and lesbians, women.'" LaTourette said. "It makes it pretty tough to win a national election if you're writing off that chunk of the electorate."