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WASHINGTON — President Donald Trump kept things cordial at a tax luncheon with Senate Republicans on Tuesday, briefly setting aside a brutal war of words with Bob Corker of Tennessee, the Senate Foreign Relations chairman, attendees said.

Senators described the tone of the meeting afterward as upbeat, with Trump complementing Mitch McConnell of Kentucky, the Senate majority leader, for his work and discussing a range of issues beyond tax cuts, including judges and infrastructure.

"We didn't hold hands and sing 'Leaving On a Jet Plane,' but it was a positive professional meeting," Sen. John Kennedy of Louisiana told reporters.

Thank you @POTUS for joining the @SenateGOP & @SenJohnBarrasso for lunch this afternoon. We are all united to help Americans with #TaxReform pic.twitter.com/Pm1z4UHaMH — Leader McConnell (@SenateMajLdr) October 24, 2017

Sen. Pat Roberts of Kansas described Trump's message on taxes as "Let’s get it done" and said the president told senators to emphasize his plan's benefits for the middle class. So far both sides are operating off only a broad framework released last month, but House leaders plan to introduce a full tax bill on Nov. 1.

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But the tensions threatening to derail the party's agenda returned after the lunch meeting in full force. Sen. Jeff Flake, R-Ariz., said on the Senate floor that he would not run for re-election in 2018 and delivered a long and emotional speech urging his colleagues to confront and denounce Trump's behavior.

Corker, who had traded insults with Trump all morning, described the lunch as "uneventful," and said he did not talk to Trump during the gathering.

The president’s visit was just the most visible part of the White House's all-out push on tax cuts; if they fail, Trump and many other Republicans believe it would spell doom for the party in next year's midterm elections. Trump called House Republicans on Sunday, saying he was glad the party was unified on the issue for a change and warning there would be a "bloodbath" in 2018 if they didn’t stick together, sources told NBC News.

"There is no amount of whatever that someone from the White House could do to affect how I might vote on something relative to the policy itself," Corker said after the meeting.

Republicans are operating with little room for error as tackle the tax code, a notoriously thorny issue they hope to complete by the end of the year.

Unless Trump can find Democratic support, he can afford to lose only two Republican votes in the Senate. Flake’s retirement means there's another senator who both loathes the president and faces no political consequences for bucking his agenda.

Sen. Thom Tillis of North Carolina entered the tax meeting with a bag of popcorn, a seeming nod to the ongoing spectacle within the party. Asked by NBC News whether his snack was for the "Corker-Trump fight," he smiled and replied, “Yes!”

Tillis was less enthusiastic about the implications of the conflict itself. "All I really want to talk about is how we get 51 votes to get tax reform done," he said.

Sen. David Perdue of Georgia, a prominent Trump supporter, said both Corker and the president were “great Americans,” but made clear he did not share his colleague’s views.

"I have a different opinion," he said. "I think this person in the White House is a person of destiny."