SCF's endorsement of businessman Matt Bevin comes two days after McConnell helped craft a compromise bill to end the government shutdown and extend the debt ceiling — a bill several conservative groups opposed that passed with the support of a minority of House Republicans.
"We know that winning this primary won't be easy," SCF Executive Director Matt Hoskins said of the Kentucky race. "Mitch McConnell has the support of the entire Washington establishment and he will do anything to hold onto power. But if people in Kentucky and all across the country rise up and demand something better, we're confident Matt Bevin can win this race."
The endorsement comes at a good time for Bevin, especially given that he struggled to raise money in the third quarter. He raised $222,000 and self-funded another $600,000 himself.
SCF announced Thursday that it would begin endorsing candidates for 2014 and shortly thereafter backed Sen. Thad Cochran's (R-Miss.) new primary challenger, state Sen. Chris McDaniel.
The Club for Growth also backed McDaniel on Thursday. As for Bevin, it said in a statement that it is withholding judgment -- while notably offering some kind words for McConnell's record.
“While we don’t always agree with Mitch McConnell, we appreciate his 84 percent lifetime score on the Club for Growth’s congressional scorecard and his steadfast support for First Amendment free speech rights," Club spokesman Barney Keller said. "We are continuing to monitor the race.”
McConnell is also a top target in the general election, where Secretary of State Alison Lundergan Grimes is the presumptive Democratic nominee and raised an impressive $2.5 million last quarter — more than McConnell's $2.3 million.
Sarah Palin has also suggested she might get involved in the Kentucky Senate primary -- presumably by backing Bevin.
McConnell spokeswoman Allison Moore responded to the SCF endorsement: "Matt Bevin now has the dubious honor of standing with a self-serving D.C. fundraising group that made its name by recruiting and promoting unelectable candidates that ensured Barack Obama a majority in the Senate. They clearly care less about Kentuckians than they do about their reputation for supporting laughably bad candidates. Now they can add a New England bailout recipient who claims he went to MIT to their roster of notable failures."
Updated at 11:48 a.m.