The group was founded in 2008 as a leadership political action committee by then-Sen. Jim DeMint (R-SC). More recently, the group has closely aligned itself with Sen. Ted Cruz (R-TX), and has relentlessly attacked McConnell, Sen. John Cornyn (R-TX) and other established Republican members of the Senate for not backing efforts to defund or repeal Obamacare fervently enough.
In addition to its high-level targeting of McConnell, the group has also heavily boosted Sen. Thad Cochran (R-MS)'s challenger state Sen. Chris McDaniel (R), essentially encouraging contested Republican primaries.
Tea party organizations like the Club for Growth and The Madison Project have also criticized Republican leadership and backed far-right candidates but the Senate Conservatives Fund has been arguably the loudest and most aggressive of such groups.
The establishment wing of the party argues that SCF's endorsements are a waste of time and resources, promote fringe candidates that may have less of a chance against Democrats in the general election and ultimately risk the goal of regaining control of the Senate. The frustration with this strategy is increasingly bubbling to the surface, and some have decided that it was time to go public with their problems with the powerful group.
Rob Collins, the executive director of the NRSC, told reporters earlier in the week that his organization is now open to spending money on its preferred, establishment candidates in Republican primaries, a signal that the NRSC is ready to go toe-to-toe with Senate Conservatives Fund around the country.
A week before McConnell's comments to the Journal, the NRSC warned Republican Senate campaigns and GOP organizations not to do business with Jamestown Associates because the group had worked with the Senate Conservatives Fund. That same report in The New York Times featured a quote from Josh Holmes, McConnell's former chief of staff who is currently working with the NRSC, comparing the Senate Conservatives Fund to someone "wandering around the country destroying the Republican Party like a drunk who tears up every bar they walk into."
"The difference this cycle is that they strolled into Mitch McConnell's bar and he doesn't throw you out, he locks the door," Holmes said.
Almost immediately after the story was published, operatives from both wings of the GOP took to attacking one another publicly on Twitter. NRSC communications director Brad Dayspring battled with former adviser to Texas Gov. Rick Perry (R) Sean Davis.
.@BDayspring And does this also mean you'll no longer do work w/ any firm that's ever been involved in a GOP primary?— Sean Davis (@seanmdav) November 1, 2013
@seanmdav it means we won't do business with organizations whose efforts do more to elect Democrats than Republicans. Period.— Brad Dayspring (@BDayspring) November 1, 2013
Dayspring has also publicly called an SCF ad that bashed McConnell for cutting a deal to end the government shutdown one of the "dumbest" of the election cycle.
Cornyn, a former NRSC chairman who so far has not attracted a primary challenge in his 2014 re-election race, has been so frustrated with SCF that he's told the Dallas Morning News that it is a "destructive element" that weakens the Republican party.
The Senate Conservatives Fund and some of its prominent supporters haven't taken the criticism lying down. Later on Friday, Senate Conservatives Fund executive director Matt Hoskins sent an email out to supporters attacking McConnell's comments to the Journal and highlighting the criticism from Holmes and others.
"Mitch McConnell can't hurt us directly so he has instructed the party to punish our vendors and our candidates," Hoskins wrote in the email.
Erick Erickson, the editor of the prominent conservative Redstate blog, defended the Senate Conservatives Fund against attacks from NRSC. He wrote that mainstream Republicans in the NRSC "declared war on conservatives" and brushed aside McConnell's claim that SCF only helped Democrats.
"It's their favorite attack these days, now that attacking SCF for raising money has proved fruitless given that this particular attack is being made by dandified lobbyists and other hangers on," Erickson wrote in a post on Friday.
Even while the Senate Conservatives Fund and the NRSC make their feuding increasingly public, Republican insiders are wary about commenting on the record about the feud.
"I think it was always pretty hot, it's been hot for a long time since they were doing this stuff," one Republican operative told TPM. "It went to a different level when they started attacking McConnell but it's been bad -- I think it's been bad for a while."
Another Republican consultant told TPM that the fighting shows that the NRSC has had enough.
"I think that in recent election cycles we've certainly seen certain Senate candidates that have certainly been seen saying and doing things that make them unelectable so I think the NRSC seems to me to be saying this cycle 'we've had enough of that' we can't cost ourselves the majority by shooting ourselves in the foot," the consultant said.