Former Alaska Gov. Sarah Palin (R) has endorsed Rep. Jeff FlakeJeffrey (Jeff) Lane FlakeHistory argues for Democratic Senate gains GOP to White House: End summit mystery The Hill's Morning Report — Trump and Congress at odds over Russia MORE (R-Ariz.) in his Senate primary, a boost for Flake as he fends off a tough challenge from wealthy businessman Wil Cardon (R).

"Jeff is a proven conservative crusader, and today I am proud to announce my support for his campaign to become the next U.S. Senator from the great state of Arizona," Palin said in a statement provided by Flake's campaign. "Credited by many as the leading anti-earmark crusader in the House, Jeff has fought hard against pork barrel spending — often times casting one of the few GOP 'no' votes on bloated spending measures. He's not afraid to 'go rogue' against his own party and its leadership; and even though he has sometimes suffered the consequences from GOP leaders for failing to toe the party line, yet he continues to fight for what is right."

Flake thanked Palin for the endorsement, calling her a "passionate conservative who has inspired many in the cause to reform Washington."

This is the latest endorsement from Palin, who had stayed largely quiet until this summer about congressional races, and — unlike in 2010 — many of her endorsements have gone to candidates favored by the party establishment. Her backing of Flake makes him the second conservative with many years in Washington facing a challenge from an outsider that she's backed — she also supported Sen. Orrin HatchOrrin Grant HatchLighthizer to testify before Senate next week as trade war ramps up Senators introduce bipartisan bill to improve IRS Senate panel advances Trump IRS nominee MORE (R-Utah) in his primary win.

She's also backed candidates without Washington experience, such as former Missouri state Treasurer Sarah Steelman (R), though Steelman is seen as a strong general election candidate and is well-liked by many in the Beltway party establishment.

Though he is expected to win his Aug. 28 primary, Flake had to work harder than some expected to beat back Cardon, who has spent millions of his own dollars attacking Flake's record on immigration. Sen. Jon Kyl (R-Ariz.) is retiring.