Senate Majority Leader Mitch McConnell on Monday told President Trump that Steve Bannon's midterm insurgency was detrimental to tax reform and other key elements of the administration's agenda.

The Kentucky Republican communicated his warning during a private lunch with the president at the White House, sources tell the Washington Examiner.

McConnell emphasized that Bannon, Trump's former chief strategist, was undermining the president's agenda with plans to recruit and finance primary challenges against Republicans who are some of his most reliable supporters in the Senate. McConnell might have made some headway.

Emerging to speak to reporters after their meeting, Trump suggested that Bannon reconsider his plans to wage war against at least a few of the incumbent Republicans on his 2018 hit list.

"I like Steve a lot. Steve is doing what Steve thinks is the right thing," Trump said, of the the nationalist flamethrower now back helming Breitbart News. "Some of the people that he may be looking at, I'm going to see if we talk him out of that, because frankly they're great people."

The moment might have been fleeting. Trump has demonstrated a knack for changing his mind, sometimes based on the last person he spoke with.

Presiding over a meeting of his Cabinet, just prior to his lunch with McConnell, the president publicly expressed sympathy for Bannon and his midterm plans. It wasn't suprising. Trump and Senate Republicans have been publicly at each other's throat for months over legislative stumbles. Bannon's self-proclaimed "war" on Senate Republicans, which has the imprimatur of the president, has ratched up the conflict.

"I can understand where Steve Bannon is coming from," Trump said, adding: "I know how he feels."

Bannon has been meeting with prospective candidates and Republican donors about his strategy to oust otherwise safe GOP incumbents in primaries next year. Bannon has said that Trump deserves a Senate more loyal to his agenda — that the Republican establishment is defying the president over policy differences.

But Bannon's top targets include Republican Sens. John Barrasso of Wyoming; Deb Fischer of Nebraska and Roger Wicker of Mississippi. Barrasso and Wicker vote with Trump 96 percent of the time. Fischer sides with the president 92 percent of the time, according to tracking from FiveThirtyEight.

None of three is known for speaking out against Trump in public.

Even occasional Trump critics like Sens. Jeff Flake, R-Ariz., and Dean Heller, R-Nev., who Bannon also is targeting, vote with the president 92 percent and 90 percent of the time, respectively. All five voted for failed legislation to repeal and replace Obamacare, although Heller was initially opposed.

None of the five is threatening to oppose tax reform.

McConnell made clear that he wouldn't back down from a fight with Bannon, whether protecting incumbents, or defending open seats from the nomination of unsavory candidates. Unsaid was that he wouldn't defer to the president, either, who has previously threatened to oppose Flake and Heller.

"My goal, as the leader of the Republican Party in the Senate, is to keep us in the majority," McConnell told reporters, with Trump looking on. "So our operating approach will be to support our incumbents, and in open seats, to seek to help nominate people who can actually win in November."

Grassroots conservatives and establishment campaign contributors are angry with Senate Republicans for the collapse of legislation to partially repeal former President Barack Obama's Affordable Care Act. Some have responded favorably to Bannon, desiring fresh leadership, retribution, or a mixture of both.

McConnell allies are questioning Bannon's motives.

Ousting senators with demonstrated loyalty to the White House isn't a viable strategy for easing passage of Trump's agenda in a chamber where the Republicans hold a razor-thing majority. They can afford to lose just two votes on 51-vote bills like tax reform if Democrats are unanimously opposed, as is typical.

Bannon's approach "would be exactly what someone would do if their only goal was to derail the Trump agenda and drain the resources of the Republican Party," one GOP insider said.

Anti-establishment figures on the Right who support Bannon, and have talked strategy with him, concede that his broader goal is dislodging McConnell as majority leader. Bannon figures that eliminating McConnell loyalists, even those who have been equally loyal to Trump's agenda, would enable him to eject the majority leader from power.

Sen. Cory Gardner of Colorado, chairman of the National Republican Senatorial Committee, his party's Senate campaign arm, shrugged off Bannon's attacks and said incumbents would be defended.

"Whoever it is that wants to run primaries, they can do that. But our guys are going to come back because they're great representatives of their state," Gardner said.