Prominent Republicans are divided in the Wisconsin's GOP Senate primary, with two candidates scrapping over conservative bona fides in the fight to take on Sen. Tammy Baldwin Tammy Suzanne BaldwinKeep teachers in the classroom Cher raised million for Biden campaign at LGBTQ-themed fundraiser Democrats seek balance in backing protests, condemning violence MORE (D-Wis.).

Marine Corps veteran Kevin Nicholson and state Sen. Leah Vukmir are both battling for the right to take on Baldwin. The eventual GOP candidate could be buoyed by 2016 Republican victories in the state.

Vukmir won a highly coveted endorsement Monday from Reince Priebus Reinhold (Reince) Richard PriebusLeaked audio shows Trump touted low Black voter turnout in 2016: report Meadows joins White House facing reelection challenges Trump names Mark Meadows as new chief of staff MORE, the former Republican National Committee (RNC) chairman and White House chief of staff who cut his political teeth in Wisconsin.

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Priebus soon attacked Nicholson, questioning his conservative credentials on talk radio. Priebus’s offensive underlines the evolving dynamics of the race, as both candidates court a very engaged GOP primary electorate.

Political newcomers have had political success in Wisconsin in the past. Sen. Ron Johnson Ronald (Ron) Harold JohnsonThe Hill's Morning Report - Sponsored by The Air Line Pilots Association - White House moves closer to Pelosi on virus relief bill Second GOP senator to quarantine after exposure to coronavirus GOP-led panel to hear from former official who said Burisma was not a factor in US policy MORE (R-Wis.) leveraged his business career into a successful Senate bid in 2010, despite having never run a political race before. And in 2016, President Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE, then a newcomer to politics, became the first Republican presidential candidate to win the state in more than 30 years.

But prominent GOP politicians such as Wisconsin Gov. Scott Walker have given grass-roots Republicans high-profile victories, too, on issues like collective bargaining.

Nicholson, who has never run for elected office before, sees himself as an outsider ready to follow in the mold of Johnson and Trump as a fresh face.

But Vukmir’s camp is happy to embrace her more than 10 years representing a staunchly conservative district in the state legislature. Vukmir’s campaign has sought to portray her as in-step with Walker and his successes.

“The fact of the matter is there’s no clear anti-establishment breakdown in this race,” said a GOP operative familiar with Wisconsin’s Senate race.

“Does Leah’s natural connection with Republican primary voters win out, or do Kevin’s resources and organization perhaps build credibility with those voters?”

That dynamic was on display in both Priebus’s endorsement and the increasingly heated rhetoric coming from both sides.

While Priebus endorsed Vukmir as a central steward of Walker’s agenda, he also went out of his way to chide Nicholson for previously being a Democrat.

Nicholson is open about his past as an active Democrat who once ran the College Democrats of America, arguing that his views have evolved and that he’s now a true Republican believer.

But Vukmir and her allies have used that past against him, fundraising off of an old quote of Nicholson criticizing former President Reagan.

“I just find this all too convenient, all too contrived, and I just don’t buy it,” Priebus said of Nicholson’s conversion to the GOP during a radio interview on Milwaukee’s 1130 WISN.

Nicholson spokesman Brandon Moody pushed back in a statement that criticized Priebus’s tenure in the White House, framing the endorsement as another favor doled out among insiders.

“Reince must have hit his head pretty hard when Trump kicked him to the curb. Of course insiders are going to protect insiders,” Moody said.

Priebus, who chaired the Wisconsin GOP before becoming head of the RNC, is expected to help Vukmir’s campaign more as things progress. That could magnify Vukmir’s connections to the party grass roots.

Charlie Sykes, a prominent former conservative radio host in the state, told The Hill that Vukmir’s long-standing relationships with Republican activists give her a “significant advantage at the moment.”

“To be an insider in Republican politics in Wisconsin means that you were part of the Scott Walker revolution ... you were part of the legislative conservative victories,” he said.

But Nicholson has done a good job at building his own base of support, looking to frame himself as an outsider ready to shake up Washington.

Nicholson entered the race in July, giving himself an early head start that allowed him to coalesce support from national groups like the Club for Growth and FreedomWorks. More recently, he won the backing of Sen. Ted Cruz Rafael (Ted) Edward CruzVideo of Lindsey Graham arguing against nominating a Supreme Court justice in an election year goes viral Sunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election Democrat on Graham video urging people to 'use my words against me': 'Done' MORE (R-Texas), a former presidential candidate.

“There’s a sense of, ‘we may need to do something different, [we] can’t just rely upon same-old and same-old,’ ” said Matt Batzel, the national executive director of American Majority.

Nicholson’s message, Batzel added, can be summed up as: “This state prefers outsiders. I’m your outsider, I’m not just the next in line.”

Not all of Nicholson’s endorsements have paid off. Nicholson won the support of former White House chief strategist Stephen Bannon, which he had hoped would boost his conservative credentials and fundraising. But that endorsement fell flat earlier this month, when Bannon and Trump fell out over Bannon remarks quoted in Michael Wolff’s book about the White House.

Still, Nicholson’s fundraising prowess and national support make him a strong contender. He outraised Vukmir in 2017, and has $500,000 cash on hand. A Vukmir spokesman told The Hill that she’d report a similar cash on hand amount.

Nicholson has a leg up in the outside money game, too. Former U.S. Ambassador to the United Nations John Bolton’s super PAC has launched a $1 million ad campaign to back Nicholson, and GOP mega-donor Richard Uihlein has put at least $3.5 million into a super PAC supporting him.

By comparison, Vukmir’s allied super PAC has raised just $1 million. But she has the support of her own mega-donor, Wisconsin native Diane Hendricks.

Nicholson allies admit that Vukmir started with some advantages, but they’re encouraged by signs that his campaign is gaining traction. Nicholson’s campaign pollster found him 7 points up on Vukmir in an early December poll, with 60 percent of likely GOP primary voters aware of him.

The battle over who can consolidate support with the conservative grass roots will be on display at the state convention in May, where both candidates will be vying for an endorsement.

Vukmir enters the race with the advantage, since delegates voting on the endorsement are likely more familiar with her. In order to win the endorsement, candidates need to get 60 percent of those delegates to support them.

It’s uncertain if either candidate will be able to get enough votes, but an endorsement from the state’s grass-roots activists can be a significant boon in the contested primary.

Nicholson and Vukmir both signed a unity pledge to support the eventual GOP nominee, a requirement to obtain a list of contact information for previous delegates.

But the GOP field could still grow, as Eric Hovde, who came in second in the 2012 GOP Senate primary, considers the race. It’s unclear whether he’ll run, but he has enough personal wealth to potentially scramble the primary field.

Democrats are hopeful that the tough talk ends up scarring whoever comes out of the primary to face Baldwin. But Sykes said Republicans would have likely rallied behind their nominee by November.

“By November, no one will remember what we are talking about now, our attention spans are so narrow,” he said.