Top Senate Republicans are firing back at Stephen Bannon amid reports that he is eyeing primary challenges to GOP incumbents who he believes haven't been supportive of President Trump, calling on both the president and his ousted chief strategist to leave elected Republicans alone.

"I wish they would focus on Democrats instead of Republicans," Senate Majority Whip John Cornyn John CornynCalls grow for Biden to expand election map in final sprint Bipartisan praise pours in after Ginsburg's death Chamber of Commerce endorses McSally for reelection MORE (R-Texas) told reporters when asked about Bannon.

Sen. John Thune John Randolph ThuneWhat Senate Republicans have said about election-year Supreme Court vacancies The Hill's 12:30 Report - Presented by Facebook - Don't expect a government check anytime soon The Hill's Morning Report - Sponsored by The Air Line Pilots Association - Trump contradicts CDC director on vaccine, masks MORE (S.D.), the No. 3 Senate Republican, added that the potential primary threats could make it harder for Republicans to hold onto their thin 52-seat majority despite a favorable map in the 2018 midterm elections.

"It does [make it harder]. And it's not particularly productive. ... We ought to stay focused on the task at hand," he told reporters.

Sources told CNN and Politico that Bannon and his allies are actively preparing for Republican primary challenges to several sitting senators, including Sen. Jeff Flake Jeffrey (Jeff) Lane FlakeJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Republican former Michigan governor says he's voting for Biden Maybe they just don't like cowboys: The president is successful, some just don't like his style MORE (R-Ariz.).

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Bannon, who returned to leading Breitbart News after exiting the White House last month, has signaled for months that he is willing to challenge GOP incumbents and punish congressional leadership for not being supportive of Trump’s agenda.

And the president, who recently cut a budget deal with Democratic leadership, has frequently lashed out publicly at GOP senators, including Flake, Sen. Bob Corker Robert (Bob) Phillips CorkerHas Congress captured Russia policy? Tennessee primary battle turns nasty for Republicans Cheney clashes with Trump MORE (Tenn.) and 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 (Ky.).

Cornyn added that Trump and his allies would be "well-advised to focus on growing our number of Republicans in the Senate rather than diminishing it."

"The president's going to need as many friendly faces around here as he can get in order to get things done," he said. "I realize that bipartisanship is important, but he shouldn't mistake a smile for support when it really counts."

The threat of intraparty fighting has frustrated congressional leaders, who are eager to avoid a repeat of 2010 and 2012, when some weak candidates defeated rivals from the GOP establishment in party primaries only to lose general elections.

McConnell has pledged that he and allied outside groups will spend money to help protect GOP incumbents running for reelection.

“We intend to play in primaries if there’s a clear choice between someone who can win in November and someone who can’t,” the majority leader said earlier this year.

Republicans face a largely favorable map heading into 2018, with Democrats defending roughly two dozen seats, including 10 in states Trump won in last year's presidential election.

Flake and Sen. Dean Heller Dean Arthur HellerOn The Trail: Democrats plan to hammer Trump on Social Security, Medicare Lobbying World Democrats spend big to put Senate in play MORE (Nev.) are the two Republican senators widely considered most vulnerable.

Meanwhile, Corker and Sen. Orrin Hatch Orrin Grant HatchBottom line Bottom line Senate GOP divided over whether they'd fill Supreme Court vacancy MORE (R-Utah) have yet to commit to running for reelection next year, and Sen. Susan Collins Susan Margaret CollinsJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally Momentum growing among Republicans for Supreme Court vote before Election Day MORE (R-Maine) is eyeing a 2018 gubernatorial bid.

Corker told reporters he has "no reason to believe" the administration would encourage a GOP primary challenger against him.