“I’ve sensed this shift in just the last couple of weeks. I think the Republicans are finally figuring out if they don’t pass this, the political consequences are going to be catastrophic,” said Stephen Moore, a senior fellow at the Heritage Foundation who is advising Mr. Trump on tax policy. “The attitude of the conservative base is, ‘If they don’t do this, they’re worthless.’”
Credit Al Drago for The New York Times
Large donor groups are particularly blunt on this point. “Passing tax reform is critical for Republican lawmakers, and they are building momentum to get it done,” said James Davis, an executive vice president at Freedom Partners, which is part of the billionaire Koch brothers’ network of political groups.
The comity of a tax cut was evident only on Tuesday, as Republicans appeared to come apart at the seams over their party’s president.
Mr. Flake announced his retirement from the Senate floor in a speech that criticized Mr. Trump and scolded other Republicans for supporting the president’s at times erratic behavior in the White House, while Mr. Corker accused Mr. Trump of “debasing” the country with his approach.
Senator Mitch McConnell, Republican of Kentucky and the majority leader, sought to bridge the gap by invoking the tax bill that is expected to be introduced in both the Senate and the House next month.
“Tax reform is what we are about,” Mr. McConnell said. “If there’s anything that unifies Republicans, it’s tax reform.”
Speaker Paul D. Ryan, Republican of Wisconsin, said that he did not think that Mr. Trump’s dispute with Mr. Corker, which sprawled across social media on Tuesday, “changes our efforts on tax reform.”
Credit Gabriella Demczuk for The New York Times
The cohesion harkens to the roots of a party that for decades identified along free-market, limited-government lines, but is now increasingly embracing the nationalistic policies of Mr. Trump. The conservative columnist Robert D. Novak once quipped that “God put the Republican Party on earth to cut taxes,” a line many Republicans still invoke today.
The effort to cut taxes was already going to be tough, given the magnitude of the business and individual income tax cuts Republicans are considering and their ability to offset the enormous cost. Finding common ground will get only more difficult as Republicans worry about their political futures and the effect on their constituents from the various tax changes under consideration.
Polling suggests Republican voters subscribe less to the tax cut philosophy than their elected representatives. A report this week from the Pew Research Center, based on polling from August, found that “Republicans were not especially unified in support of tax cuts,” said Carroll Doherty, the center’s director of political research. “Over all, there was some division of opinion even among conservative Republicans, with about half supporting lower tax rates for corporations.”
A September poll from the online survey company SurveyMonkey found that three-quarters of Republicans and Republican-leaning independents approve of cutting corporate taxes, which is the centerpiece of the tax plan Republicans are expected to put forth next week. The same poll, and a related October SurveyMonkey survey, found a divide in the Republican Party on the issue: Republican voters who approve of Mr. Trump were far more likely to approve of corporate tax cuts and to say that they believe their individual taxes will fall next year.
The divisions in the party do not, at this point, appear to imperil the tax-cutting effort. Mr. Corker is widely viewed as having prevailed in pushing for specific limits on the cost of any tax cuts in the Republican budget. And Mr. Flake — Tuesday diatribe aside — is still viewed as a likely “yes” on whatever tax bill makes it to the Senate floor.
Still, the baby has yet to be born, and it is an open question whether its arrival will patch the divisions that are threatening to rupture the party.