A small group of Republican strategists opposed to President Trump, branding themselves Defending Democracy Together, quietly conducted polling and focus groups last fall to gauge whether the president was vulnerable to a primary challenge in 2020. Assembling a presentation for sympathetic political donors, they listed points of weakness for Mr. Trump such as “tweeting/temperament” and “criminality/corruption.”
The group concluded that Mr. Trump’s scandals were not yet badly damaging him with Republican-leaning voters: “Even relatively high information voters aren’t paying particularly close attention to day-to-day scandals,” the presentation stated. But it added that there was “room to educate voters” on the subject.
Michael D. Cohen, Mr. Trump’s former lawyer, may have begun that education on Wednesday.
With Mr. Cohen’s appearance before a House committee, the public airing of ethical transgressions by Mr. Trump reached a new phase, one that may be harder to ignore for friends and foes alike. The spectacle of Mr. Trump’s onetime enforcer denouncing him in televised proceedings, detailing a catalog of allegations of cruelty and crimes, signaled the pressure the president’s already strained coalition could feel in the coming months as Congress scrutinizes him, and as the special counsel Robert S. Mueller III completes his investigation.
Republicans still find it difficult to imagine that Mr. Trump’s electoral base would ever desert him, though they acknowledge that bond may soon be tested as never before. Mr. Trump’s core supporters — numbering about two in five American voters, polls suggest — have stayed with him through revelations of financial and sexual impropriety, painful electoral setbacks and the longest government shutdown in history.
Robert Blizzard, a Republican pollster, said public opinion of Mr. Trump had proved remarkably fixed over time, “despite over two years of countless stories about Russia, Stormy Daniels, Michael Cohen and others.” He dismissed the possibility that Mr. Cohen would shift opinion on either the left or the right.
“The president’s base is rock solid, and his opposition is equally rock solid,” Mr. Blizzard said.
Ralph Reed, a longtime evangelical leader, said Mr. Trump’s record of delivering on conservative priorities had effectively cemented his own party in place, fostering particular loyalty among Christian conservatives with two Supreme Court appointments and efforts to restrict abortion rights.
“He made a set of promises and he not only kept them — he is in many cases exceeding them,” Mr. Reed said.
Mr. Trump may be demanding more and more loyalty from his political base as the adversity he faces in Washington grows more intensely personal. Even before he asks conservatives to secure him a second term in 2020, Mr. Trump will be relying on the right flank of the G.O.P. to keep congressional Republicans in line, as a Democratic-led House conducts intrusive investigations.
Yet in the electoral arena, Mr. Trump’s political survival has long depended on his ability to marry the unbending support of his fiercest followers with the ambivalent backing of more traditional right-of-center voters — people who view him as a distasteful character but favor his economic policies, or who preferred him over Hillary Clinton in 2016.
Many voters in the latter group defected to vote for Democrats in the midterm elections or stayed home, helping deliver the House into Democratic hands. Should the same thing happen in 2020, it would be very difficult for Mr. Trump to assemble the Electoral College votes he needs to win a second term.
It may grow more difficult for Mr. Trump to reforge his 2016 coalition if he faces protracted humiliation of the sort inflicted by Mr. Cohen. In addition to denouncing Mr. Trump as a racist, a liar and a habitual business cheat, Mr. Cohen hinted at the gravity of an investigation by federal prosecutors in New York. And he may have pointed the way toward potential future hearings involving Mr. Trump’s employees and even family members.
Some Republicans who have been critical of Mr. Trump have suggested that a turbulent first half of 2019 could create an opening for other Republicans to enter the presidential race, if prosecutors allege that Mr. Trump has broken laws or if the president begins to appear so politically weak that the party fears it could lose the 2020 election in a rout.
Gov. Larry Hogan of Maryland, a moderate Republican who is weighing a primary challenge to Mr. Trump, suggested in a recent interview that the president’s strength as a candidate was a big question mark and speculated that Mr. Trump might ultimately choose not to seek another term.
“He’s pretty strong in a Republican primary at this time,” Mr. Hogan said, adding vaguely, “I don’t know what’s going to happen over the next several months.”
Mr. Hogan suggested that Mr. Trump’s command of the Republican base could be attributed mainly to conservatives’ revulsion with the Democratic Party, more than their thoroughgoing affection for Mr. Trump.
“He’s the president and Republicans are saying, ‘Well, we support the Republican president and we don’t like some of these far-left Democratic alternatives,’” Mr. Hogan said.
For most Americans who view Mr. Trump with distaste or worse, Mr. Cohen’s testimony most likely served to confirm their darkest views of the president. A majority of the country has viewed Mr. Trump from the start as a person of low character and limited aptitude for leadership, traits Mr. Cohen highlighted at exhaustive length.
So far, Democrats have largely acted as if Mr. Trump’s personal defects are so well known that they require scant elaboration. That was the strategy most Democratic candidates adopted in the key midterm elections, trusting Mr. Trump’s unpopularity to weigh down Republicans but focusing chiefly on issues like health care.
Several of the leading 2020 candidates have made references to the president’s tribulations, but mainly in the form of passing applause lines. Senator Kamala Harris of California alludes to Mr. Trump’s scandals and her background as a district attorney by urging Democrats to nominate someone who can “prosecute the case” against Mr. Trump.” On a recent trip to Iowa, Senator Elizabeth Warren of Massachusetts joked that Mr. Trump “may not even be a free person” at the time of the next election.
Republicans are quick to point out that no presidential race is a simple up-or-down vote on the incumbent, and they remain hopeful that Democrats will nominate a candidate aligned with the far left who could alienate some moderates and induce them to give new consideration to Mr. Trump.
Henry Barbour, an influential member of the Republican National Committee from Mississippi, said he did not believe events like Mr. Cohen’s testimony would affect his support within the G.O.P., noting that Republicans did not think Mr. Trump was “a Boy Scout when they voted for him in ’16.”
“Ultimately, this is going to be a choice between Donald Trump and somebody who sounds like they think the U.S. should be a socialist country,” Mr. Barbour said.
But party strategists like Mr. Barbour acknowledge the president’s misconduct has made him vulnerable to defeat, at least if Democrats put forward a broadly appealing candidate.
“If Democrats nominated a moderate from the heartland of the country, then it would be a much tougher race,” Mr. Barbour said.
One challenge for Mr. Trump, however, is that he will have no easy foil until Democrats settle on their presidential nominee sometime next year.
“Trump is always better when he has somebody to pick on,” said Wes Gullett, a Republican strategist based in Arizona, adding wryly, “If Democrats were smart, they would move their convention back until about Oct. 15.”