“The million-dollar question is, will they vote, will they sit it out — or will they vote for Joe Biden?” former Gov. Jim Hodges, a South Carolina Democrat, said of Ms. Haley’s centrist supporters in the state. “A moderate Republican voter in Charleston is not all that different than a moderate Republican voter in the Milwaukee suburbs.”

In recent interviews with nearly 40 Haley supporters across South Carolina’s Lowcountry, primarily conducted in historically more moderate enclaves of the state, many fell into what pollsters call the “double haters” camp — voters who don’t like either expected nominee.

“It just infuriates me that we have the choices that we do,” said Roberta Gilman, a former teacher and a resident of affluent Mount Pleasant, S.C., who is in her 70s.

Roughly half of those interviewed, including Ms. Gilman, said that in a Biden-Trump matchup, they would side with the Republican, while expressing varying degrees of discomfort. That number would almost certainly be higher in the actual results of the general election, after Americans have retreated further into partisan corners.

Others, like Ms. Gramling, made it clear that Mr. Trump — who has driven many moderate and suburban voters out of his party over the last eight years — faces even graver challenges with those Americans now.

“Everything about him bothers me — his arrogance, his lack of support of the military,” said Ms. Gramling, who was also a teacher. She supported Mr. Trump in 2016 before backing Mr. Biden in 2020 and would back the Democrat again over Mr. Trump. “Everything that he does is uncalled for.”

Here’s how some of these Haley voters are thinking through a choice they hope they won’t have to make:

The drifting-from-Trump voters

America has very few persuadable voters left, and that may be especially true in a Biden-Trump rematch. Both men have been on the national stage for decades, and voters formed opinions of them long ago.

But a few Haley voters who said they had supported Mr. Trump in 2020 stressed that they would not do so again. They cited his behavior after his defeat, including his election denialism that led to the Jan. 6, 2021, attack on the Capitol.

Any erosion in 2020 support for either Mr. Trump or Mr. Biden could prove consequential this year, especially with third-party candidates in the mix.

“If he was my choice, or Biden was my choice, I would have no choice,” said Julia Trout, 55, of Mount Pleasant, adding that she had always voted for the Republican ticket but would probably sit out a Biden-Trump matchup.

Asked what had changed her views on Mr. Trump since 2020, she replied, “the insurrection.”

“What would we do if we had another civil war?” she said. “If we can support something like that insurrection, there’s no telling what could happen.”

Mr. Trump, she said, is not a politician — “he’s a tyrant.”

Jeff Heikkinen, 41, a caddie who lives in Summerville, S.C., said he had supported Mr. Trump in past elections but was troubled by his personal attacks on Ms. Haley involving her husband, a National Guardsman, and her background as the daughter of Indian immigrants.

“He’s just trying so hard to separate people, making fun of her husband rather than be a grown-up,” he said. If his choices were Mr. Biden and Mr. Trump, he added, “I probably wouldn’t vote — I’m just that disenchanted with both of them.”

Joy Hunter, 64, of Summerville, declined to share how she had voted in the last election — though she said she had “never voted Democrat” — but ruled out supporting Mr. Trump this year, citing, in part, the Capitol riot.

“I know people say, ‘Just ignore his character and instead focus on what he’s done,’ but I don’t know that you can separate entirely a person’s character from their policies,” Ms. Hunter said. She added of Ms. Haley, “I’m going to beg her not to drop out.”

The cognitive-dissonance Republicans

Andrew Osborne, 58, a retired business owner from Summerville, said he disliked Mr. Trump “with a passion,” declaring: “I could not take four more years of him. In fact, I’d probably consider leaving the country if that was our alternative.”

He would theoretically consider a Democrat, he said, because of his moderate positions on issues like abortion rights and gun rights.

But in a choice between Mr. Trump and Mr. Biden, he said, he would still vote for the Republican, citing concerns about Mr. Biden’s age.

Mr. Osborne pointed to the release of a special counsel’s report that described Mr. Biden as a “well-meaning, elderly man with a poor memory” and a verbal slip Mr. Biden made soon after, referring to the president of Egypt as the “president of Mexico.”

“He’s a similar age to my father-in-law, and I love him to death, but I wouldn’t trust him to make me a cup of coffee,” Mr. Osborne said. “This is the commander in chief of the last superpower.”

The interviews highlighted just how polarized the nation has become and underscored the limits of Mr. Biden’s bipartisan appeal, something he had in small but significant measures in 2020.

Joe Mayo, 72, a retired operator at a nuclear power plant who now lives in Mount Pleasant, called Mr. Trump “arrogant” and “stupid” and said that he did not “represent my thoughts about the way business should be done.”

But if he is the Republican nominee, Mr. Mayo said, he will still support him, because “the Democratic Party is worse than Donald Trump.”

He is hardly alone: A recent NPR/PBS NewsHour/Marist Poll found that 82 percent of Haley voters overall said they would back Mr. Trump if he faced Mr. Biden.

Lynn Harrison Dyer, a businesswoman in her 60s from Mount Pleasant, noted proudly that she was the daughter of a World War II veteran and said she was supporting Ms. Haley in part because she “honors the military.”

Mr. Trump, she noted, has denigrated veterans.

“That goes against everything I truly believe in,” she said. “I honor and respect the military.”

But in a Trump-Biden contest, she said, she would support Mr. Trump, describing worries about Mr. Biden’s age.

Mr. Biden is 81 and Mr. Trump is 77, but polls show the age issue