Updated at 4:44 p.m. ET with a response from Stewart's campaign.

The main political arm of the industrial Koch brothers group, Americans for Prosperity, said it won't endorse or back Republican Senate candidate Corey Stewart in the November midterm election, The Daily Progress reported.

What's the story?

The libertarian group, which typically supports conservative candidates in swing states such as Virginia, announced it wouldn't deploy activists or run any ads supporting Stewart in his campaign to unseat incumbent Democrat Sen. Tim Kaine. Stewart barely clinched the nomination in Tuesday's Republican primary.

"We will continue to stand with those who support policies that will enable people to improve their lives and communities," AFP Virginia State Director JC Hernandez said.

The group previously endorsed Virginia GOP state Delegate Nick Freitas, who lost to Stewart by less than 2 percent of the vote in the primary Tuesday.

“Nick Freitas has earned our support by backing up his rhetoric with a record of leadership on tough issues,” Hernandez told The Washington Post in a statement. “We stand behind our decision to support a principled lawmaker who has a track record of fighting for policies that would help Virginians improve their lives."

What does Stewart's campaign say?

What about Stewart's controversial tactics?

Stewart's controversial tactics and past connections to anti-Semitic Paul Nehlen and white nationalist Jason Kessler have also cost him support from other GOP groups including the Senate Republicans campaign arm.

Stewart most recently accused Kaine of being at the "center" of the FBI scandal.

“I’ll tell you something, I really do believe that Tim Kaine has been at the center of all this stuff that you’re seeing with regard to the FBI. You know, the whole problem is having the FBI spying by a federal agency on a presidential campaign,” Stewart said during an interview Wednesday on CNN.

Stewart's comments about Kaine and the FBI start at 2:15 in the clip.

What else?

Stewart has gained a following for his crackdown on illegal immigration in Prince William County. He also wants to focus on jobs, reducing corporate taxes and repealing and replacing Obamacare.

He said he plans to wage a "vicious" campaign against Kaine, who's expected to win re-election.

"Virginians will have a choice between ruthless and vicious and an upbeat problem solver," Kaine said, according to WHSV-TV.