An aide to DeMint said the PAC puts money behind every candidate it endorses — Flake included.

Although Flake is the clear front-runner in the GOP primary for retiring Sen. Jon Kyl’s (R-Ariz.) seat, he faces a well-funded opponent in Wil Cardon, the real estate investor who, as DeMint noted, has pledged not to be outspent in the race.

“Just recently, Wil Cardon directly attacked your freedom to engage in the political process. He called for a ban on campaign spending by citizen groups like the Senate Conservatives Fund,” DeMint wrote. “He says you should be silenced and that your constitutional right to make your voice heard should be taken away.”

But Flake could face an even tougher challenge in the general election from Democrat Richard Carmona, the former U.S. surgeon general under President George W. Bush. DeMint’s endorsement signals that Republicans might now be taking Carmona’s challenge seriously in a state that Democrats are eager to demonstrate they can put in play.

A conservative kingmaker and Tea Party favorite, DeMint has been actively supporting Senate candidates this cycle, including Josh Mandel in Ohio, Mark Neumann in Wisconsin and Don Stenberg in Nebraska.