Republicans on Capitol Hill fear that Stephen Bannon’s plan to wage primary challenges against incumbent senators will put their majority at risk in 2018.

Senate GOP aides warn that Bannon, Trump’s former chief strategist, is not motivated by a desire to advance President Trump’s agenda, but instead by a quest to remake the GOP in his own, nationalist image.

“If anyone misunderstands what Steve Bannon’s goal is, they have to open their eyes. He doesn’t care if we win or lose the Senate. He doesn’t care about the consequences for the president,” said one Senate Republican aide.

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“Mr. Bannon, it seems clear, does not care about Republicans maintaining their majority in either chamber. He’s putting his former boss’s agenda on the line in his quest of take over and destroy the Republican Party,” the source added.

Bannon did not respond to an email summarizing the criticism of Senate GOP aides.

The former White House adviser this week said he is working to field primary challengers against incumbents such as Sens. Roger Wicker Roger Frederick WickerHillicon Valley: DOJ indicts Chinese, Malaysian hackers accused of targeting over 100 organizations | GOP senators raise concerns over Oracle-TikTok deal | QAnon awareness jumps in new poll Shakespeare Theatre Company goes virtual for 'Will on the Hill...or Won't They?' Republican Senators raise concerns over Oracle-TikTok deal MORE (R-Miss.), Deb Fischer Debra (Deb) Strobel FischerHillicon Valley: Election officials prepare for new Russian interference battle | 'Markeyverse' of online fans helps take down a Kennedy | GOP senators unveil bill to update tech liability protections Google, Apple, eBay to meet virtually with lawmakers for tech group's annual fly-in Congress botched the CFPB's leadership — here's how to fix it MORE (R-Neb.), Orrin Hatch Orrin Grant HatchBottom line Bottom line Senate GOP divided over whether they'd fill Supreme Court vacancy MORE (R-Utah) and John Barrasso John Anthony BarrassoOVERNIGHT ENERGY: Democrats push resolution to battle climate change, sluggish economy and racial injustice | Senators reach compromise on greenhouse gas amendment stalling energy bill | Trump courts Florida voters with offshore drilling moratorium Senators reach compromise on greenhouse gas amendment stalling bipartisan energy bill The Hill's Morning Report - Sponsored by National Industries for the Blind - Trump, Biden battle over vaccine, economy; Congress returns MORE (R-Wyo.). None are considered at risk of losing their reelection races.

“Nobody is safe. We are coming after all of them, and we’re going to win,” Bannon said Monday on Fox News’s “Hannity.”

The threat from Bannon is just the latest headache for Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellMomentum growing among Republicans for Supreme Court vote before Election Day Trump expects to nominate woman to replace Ginsburg next week Video of Lindsey Graham arguing against nominating a Supreme Court justice in an election year goes viral MORE (R-Ky.) after a frustrating summer where he took heavy fire from the right and from his own president.

McConnell should have little to worry about in 2018, given that Democrats are defending 25 seats, compared with only nine for Republicans.

But Trump’s unpopularity and the possibility of brutal intraparty primary battles are threatening to scramble the map.

The veteran election forecaster Charlie Cook this week said Republicans have only an even chance of holding the majority despite their advantages.

“Given their current disarray, Republicans will need to fight hard to gain any new seats, and losing one or two of their own seats would put their majority in jeopardy,” Cook wrote in the National Journal.

A second Senate Republican aide warned that the National Republican Senatorial Committee (NRSC) might have to divert resources away from trying to capture Democratic-held seats in 10 states that Trump carried last year.

“Every dollar the NRSC puts into protecting Republican incumbents is one less dollar that can be used to challenge Democrats,” the aide said.

A Senate Republican strategist cautioned, however, that it is too soon to know what impact Bannon might have on next year’s primaries, noting that he will have to raise a lot of money to compete with leadership-allied fundraising committees.

Conservative activists are undeterred, arguing that Republicans in Washington have become an impediment to Trump’s agenda.

Bannon told CBS’s “60 Minutes” last month that the GOP establishment is “trying to nullify” the 2016 election and “do not support the president’s program.”

“It’s an open secret on Capitol Hill. Everybody in this city knows it,” he said.

Judson Phillips, the founder of Tea Party Nation, said Bannon is feeding on the frustrations of the GOP’s conservative base. A nine-month effort to repeal and replace ObamaCare fell apart last month, leaving the party without a major legislative accomplishment for the start of Trump’s presidency.

“The Republicans said start electing us and we’re going to change things. Well, they have the House, the Senate and the White House, and ObamaCare’s not repealed, tax reform is not being done and the wall is not being built,” he said.

“After all these years of promises the GOP is unwilling or unable to stand and deliver and the base is not going to tolerate it,” he said.

But Senate Republican aides say Bannon is simply making it tougher for Republicans to cut deals on taxes, spending and other issues.

“It makes it harder to enact the president’s agenda,” said the second Senate Republican aide.

Bannon’s clout with the base grew last month after he helped former judge Roy Moore defeat incumbent Sen. Luther Strange Luther Johnson StrangeSessions hits back at Trump days ahead of Alabama Senate runoff The biggest political upsets of the decade State 'certificate of need' laws need to go MORE in an Alabama Republican runoff election.

The Senate Leadership Fund, a super PAC allied with McConnell, spent more than $10 million to help Strange.

Now Bannon is setting his sights on Barrasso, Hatch and Fischer.

The possibility of a challenge from the right could make it tougher for Hatch, the chairman of the Senate Finance Committee, to strike a deal with Democrats on taxes or to reauthorize the Children’s Health Insurance Program, Senate GOP aides warn.

Those aides say Bannon’s campaign also casts a cloud over bipartisan negotiations to stabilize the individual insurance market, which some lawmakers say is needed to help constituents living in areas of the country where private insurers have pulled out.

Conservative strategists, however, are applauding the pressure from Bannon.

They say it will give Republicans more incentive to back Trump’s priorities, such as construction of a wall along the U.S.-Mexico border, which has made little headway in Congress this year.

“It will make some of these Senate members look over their shoulders and worry whether they’re voting conservative or not,” said Brian Darling, a conservative strategist and former Senate Republican aide.

“Primaries are always proved to move Republicans more to the right because they’re more worried about a primary challenge than a general election,” he added.