Just a few months ago, the Republican presidential primary seemed as if it might include a frank and vigorous debate about the leadership and limitations of Donald J. Trump.
But any appetite for criticism of Mr. Trump among Republicans has nearly evaporated in a very short time. Voters rallied around him after his criminal indictment in March on charges related to hush money for a porn star, and potential rivals have faltered, with few willing to take direct aim at the former president and front-runner for the nomination.
In a live town hall on CNN on Wednesday, the cheers for every falsehood and insult that Mr. Trump uttered under tough questioning by a moderator showed there was little to no daylight between Mr. Trump and the Republican base. A quirky effort to disrupt the love-in by Chris Christie — a potential rival who bought Facebook ads to supply audience members with skeptical questions such as “Why are you afraid of debating?” — went nowhere.
In surveys and focus groups, a fair share of Republican voters say that they would prefer a less polarizing, more electable nominee. But a near taboo against criticizing Mr. Trump has made it hard for rivals, apart from Mr. Christie and one or two others near the bottom of polls, to stand out.
In what looks like a rerun of the 2016 Republican primary, almost none of Mr. Trump’s competitors have openly gone after him, despite his glaring vulnerabilities. Instead, they are hoping — now as then — that he will somehow self-destruct, leaving them to inherit his voters.
After a jury found Mr. Trump liable for sexual abuse and defamation of the writer E. Jean Carroll on Tuesday, Mike Pence, the former vice president, who is weighing a 2024 campaign, declined to criticize Mr. Trump. In an interview with NBC News, Mr. Pence said it was “just one more story focusing on my former running mate that I know is a great fascination to members of the national media, but I just don’t think it’s where the American people are focused.”
Other 2024 candidates either defended Mr. Trump, such as the entrepreneur Vivek Ramaswamy, or played down the verdict, including Nikki Haley, the former South Carolina governor. Ms. Haley, who announced her candidacy in February, even defended Mr. Trump this week for threatening to skip Republican primary debates. “With the numbers he has now, why would he go get on a debate stage and risk that?” she said.
Only two 2024 hopefuls found the verdict in the Carroll case to be disqualifying for a would-be president: Mr. Christie and Asa Hutchinson, the former Arkansas governor. Mr. Hutchinson criticized Mr. Trump’s “contempt for the rule of law.”
Several months ago, polling had suggested Mr. Trump could be a potentially weak candidate, with only 25 to 35 percent support from Republican voters in high-quality surveys. The Republican National Committee promised an autopsy of the 2022 midterms that was expected to address Mr. Trump’s role in the party’s surprising losses.
But today, the lane in the Republican primary for a candidate who is openly critical of Mr. Trump seems to be closing.
Mr. Hutchinson’s long-shot campaign has failed to gain notice. Mr. Christie, the former governor of New Jersey, who has promised a decision this month on whether he will run, also has yet to generate much interest. Even the occasionally critical Mr. Pence, who mildly suggested Mr. Trump would be “accountable” to history for the Jan. 6 attack on the Capitol, is struggling for affirmation from the Republican base.
And the R.N.C. autopsy of the midterms? A draft reportedly did not mention Mr. Trump at all.
David Kochel, a Republican strategist who advised Jeb Bush when he ran against Mr. Trump in 2016, said there was no opportunity for a candidate openly critical of Mr. Trump in the 2024 primary.
“Voters have seen Trump as the most attacked president of their lifetimes, and they have an allergic reaction to one of their own doing it,” Mr. Kochel said. “He’s built up these incredible antibodies, in part stemming from how the base perceives he has been treated.”
A CBS News poll released this month found that among likely Republican primary voters, only an insignificant handful, 7 percent, wanted a candidate who “criticizes Trump.”
The three candidates whom voters are the least open to considering, the survey found, are those who have criticized Mr. Trump to varying degrees: Mr. Christie, Mr. Hutchinson and Mr. Pence.
David Carney, a Republican strategist in New Hampshire, said he had expected the race to be more competitive by now, but a turning point occurred in March with Mr. Trump’s indictment in New York.
“It fell into the president’s narrative of the past five years,” Mr. Carney said, referring to Mr. Trump’s portrayal of himself as a victim of a criminal justice system out to get him. Mr. Carney described what he called a “boomerang” effect on Republican primary polls. “They’re beating up your guy — there’s a rallying around the flag.”
Mr. Trump’s rivals could still see a surge in support between now and next year’s first primary contests, but for the time being he is dominating all challengers. A polling average shows him with a 30-point lead over his closest rival, Gov. Ron DeSantis of Florida, who has yet to formally announce his run. All other candidates, declared and potential, are distant afterthoughts in the race, for now.
The former president is insulated from criticism, strategists said, because of the intense and dug-in partisanship of the Republican base, and because many of those voters get information only from right-wing sources, which have minimized the Jan. 6 attack and obscured Mr. Trump’s 2020 loss.
“They barely have access to the truth,” said Sarah Longwell, an anti-Trump Republican strategist. Ms. Longwell, who hosts a podcast about Republican voters called “The Focus Group,” said a sizable share of primary voters wanted to move on from Mr. Trump.
Mr. Christie, the most sharply critical 2024 hopeful of Mr. Trump, recently attacked the former president, calling him “a child” for denying the 2020 election results and cowardly for suggesting he might duck Republican debates.
But when Mr. Christie tested the electoral waters during visits to New Hampshire the past two months, including at the same college where Mr. Trump’s town hall took place on Wednesday, his crowds seemed tilted toward independents and even Democrats, including those who knew him as the house conservative on ABC News.
One element that may factor in Mr. Christie’s calculus: The New Hampshire primary next year could favor an anti-Trump Republican because of an influx of independent voters. Because Democrats chose South Carolina as their first nominating state — and because President Biden may not appear on the New Hampshire ballot or campaign in the state — up to 100,000 independents are expected to cast ballots in the Republican race, where they could tilt the results.
“Independents are open to voting for a Republican candidate,” said Matt Mowers, who served as Mr. Christie’s New Hampshire state director in 2016, “but they aren’t open to voting for a crazy Republican.”