Americans for Prosperity President Tim Phillips is throwing his support behind Virginia Del. Barbara ComstockBarbara Jean ComstockElection Countdown: Minnesota Dems worry Ellison allegations could cost them key race | Dems struggle to mobilize Latino voters | Takeaways from Tennessee Senate debate | Poll puts Cruz up 9 in Texas GOP lawmaker suggests male Dem leaked Ford’s confidential letter Dems look to women to take back the House after Kavanaugh fight MORE (R) in her campaign for retiring Rep. Frank WolfFrank Rudolph WolfVulnerable Republican keeps focus as Democrats highlight Trump Bolton could be the first national security chief to prioritize religious freedom House votes to mandate sexual harassment training for members and staff MORE's (R-Va.) seat.

Phillips, the national head of the powerful conservative group, is also a resident of Comstock's Northern Virginia congressional district. His endorsement gives her a major credibility boost with Tea Party activists and should assuage some Republicans worried a messy primary could cost them the competitive seat. 

"Barbara Comstock is exactly the kind of leader we need representing the 10th District — conservative, articulate, willing to fight for our principles, and capable of putting together a winning campaign. I'm proud to support her," he says in a statement first shared with The Hill.

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Phillips's endorsement is from him personally — Americans for Prosperity, the billionaire Koch brothers' main vehicle for backing conservatives, doesn't endorse candidates. But it could give a boost on the right to Comstock, a longtime Republican activist and GOP establishment's favorite to succeed Wolf.

Comstock is a former Wolf staffer who was also a surrogate for the presidential campaigns of President George W. Bush and Mitt Romney. She's facing Virginia state Sen. Dick Black (R), a controversial social conservative who national Republican strategists worry could cost the party the GOP-leaning seat, if he is the nominee.

Comstock has been busy working to unite the wings of the GOP. She's already won support from both establishment Republicans and movement conservatives — Romney and conservative radio star Mark Levin have both endorsed her campaign.