Nikki R. Haley, a former United Nations ambassador under President Donald J. Trump who left the administration without the drama or ill will that marred most of its high-level departures, sharply criticized her former boss in an interview published on Friday, saying that she was “disgusted” by his conduct on Jan. 6, the day of the Capitol riot.

Ms. Haley, 49, who is widely believed to be considering a run for president in 2024, told Politico she did not believe that the former president would remain a dominant force within the Republican Party or that he would seek office again, arguing that he had “lost any sort of political viability.”

“I don’t think he’s going to be in the picture,” Ms. Haley said. “I don’t think he can. He’s fallen so far.”

Ms. Haley’s comments predictably prompted a backlash from Mr. Trump’s loyal base of support, a constituency that most Republican office holders continue to try to appease — and one that she had assiduously tried to avoid offending since leaving his administration at the end of 2018.

Before her latest comments became public, Ms. Haley seemed to realize that they would go too far for many Republicans. And it was not long before she bowed to the reality of Mr. Trump’s enduring power within the party. In an interview with Laura Ingraham of Fox News that was broadcast late last month — after Ms. Haley had spoken to Politico but before the article was published — Ms. Haley muted her criticism of the former president considerably.

“At some point, I mean, give the man a break,” she said, condemning Democrats for pursuing a second impeachment against him for instigating the Jan. 6 assault on the Capitol. “I mean, move on.” She added: “Does he deserve to be impeached? Absolutely not.”

But the storming of the Capitol last month, and Mr. Trump’s role in inciting it with repeated, false claims of ballot-rigging in the November election, caused Ms. Haley to reassess her relationship with the former president. Her tone changed markedly between interviews with Politico in December and January. At first, she refused to acknowledge that Mr. Trump was doing anything reckless by refusing to concede. She said that he genuinely believed he had not lost, and she would not acknowledge that his actions since the November election were irresponsible.

And she wrongly predicted that Mr. Trump would “go on his way” once he had exhausted his legal options.

But after Jan. 6, Ms. Haley told the publication that she had previously urged Mr. Trump to be more “careful” with his words, to no avail.

“He went down a path he shouldn’t have,” she said, referring to his deception about the election. “And we shouldn’t have followed him, and we shouldn’t have listened to him. And we can’t let that ever happen again.”

In that moment, Ms. Haley’s remarks showed that she was willing to entertain a political proposition that most other Republicans with eyes on the White House had not dared to utter publicly: that Mr. Trump’s hold over the G.O.P. base will loosen, and that he will not be the kingmaker many have predicted.

However calibrated or qualified, Ms. Haley’s approach is a departure from that of other conservatives who are believed to harbor ambitions for higher office. Senator Josh Hawley of Missouri, who lent credibility to Mr. Trump’s voter fraud claims, has refused to acknowledge that his own actions played any role in inciting violence on Jan. 6. And former Vice President Mike Pence has said nothing publicly since being forced to flee the Senate chamber under armed guard as rioters stormed the Capitol, encouraged in part by Mr. Trump’s attacks against the vice president on Twitter for not interfering with the certification of the election.

Ms. Haley was especially pointed about Mr. Trump’s treatment of Mr. Pence, sounding almost dismissive of the former president as she expressed her dismay. “Mike has been nothing but loyal to that man,” she said.

Some Republicans said that Ms. Haley’s comments were simply acknowledging reality. As a politician who is more comfortable with the establishment wing of the G.O.P., she has not always had the trust of Mr. Trump’s base. And in a crowded 2024 presidential primary, she would face stiff competition for those votes.

“You didn’t have to be clairvoyant to see which way Nikki Haley would go once Donald Trump lost,” said Sam Nunberg, a consultant who worked for Mr. Trump. “She was never going to be able to take the Trump mantle.”

To other Republicans, her words of regret were too little, too late given her earlier deference toward Mr. Trump. Representative Adam Kinzinger of Illinois, who has become one of the most outspoken critics of his party since the Capitol attack, accused Ms. Haley of playing “both sides.” On Twitter, he urged her to “Pick Country First or Trump First.”

This is not Ms. Haley’s first reversal on Mr. Trump. Like many leaders of her party, she initially opposed him when he ran for the Republican nomination in 2016. At the time, she was the governor of South Carolina, and she endorsed Senator Marco Rubio of Florida ahead of her state’s pivotal primary. Mr. Trump still won, finishing ahead of Mr. Rubio by 10 percentage points.

But she redeemed herself in the eyes of many Republican voters by signing on to work in the Trump administration, showing how quickly old slights can be forgiven by the former president and his supporters.

Voters may indeed forgive and forget altogether — which is something that critics of Mr. Trump warned would allow Republicans to go unpunished for encouraging him as he undermined faith in American democracy.

“When I got into politics, I was told you could get away with a lot because voters have short-term memories,” said Denver Riggleman, a former Republican congressman from Virginia who has been highly critical of his party’s silence as Mr. Trump spread disinformation about the election.

“What the Nikki Haleys, Ted Cruzes, Josh Hawleys of the world are relying on,” he added, “is the short-term memory of voters.”