“I think it’s completely destructive,” Cornyn, the Texas Republican and Senate minority whip, told POLITICO. “They are spending most of their money going after Republicans and making it harder for us to nominate and elect Republicans and regain the majority.”

The conservative organization is part of a tight-knit circle of third-party groups ratcheting up the GOP vs. GOP warfare that has consumed Republicans since the rise of the tea party in the 2010 midterm elections. The activists say without purist conservative lawmakers, the Republican Party implicitly supports Obama policies by working with Democrats. But GOP senators argue that the party needs to expand its tent and will occasionally need to compromise to work in a divided Washington.

“Isn’t it interesting that every dollar that is spent [attacking] good conservative Republicans … is a dollar that isn’t spent on winning the majority?” said Sen. Tom Coburn (R-Okla.), a one-time close ally of SCF founder, former Sen. Jim DeMint (R-S.C.). “If your strategy is to think that you can get 60 hard-core conservative senators in this country, I don’t think it works.”