Nikki Haley says her momentum 'is real,' but do Republican voters want someone not named Trump?

A winnowing field of Republican presidential candidates are working feverishly to close the polling gap between themselves and Donald Trump -- among them is former U.N. Ambassador Nikki Haley, whose support has steadily ticked up as an alternative to the former president.

Despite an unprecedented number of legal troubles for a presidential candidate and criticism that his rhetoric has sometimes echoed dictators of the past, all of which he denies, Trump remains largely popular with the country's conservative electorate.

With voting set to start in the 2024 Republican primary as soon as Jan. 15, in Iowa, Trump's challengers find themselves with less and less time to convince voters to support someone other than him.

Haley, a former South Carolina governor, has seen her own poll numbers and donor support continue to grow. She is now duking it out with Florida Gov. Ron DeSantis for second place.

Veteran Iowa strategist David Kochel said that Haley's emergence in the race as "the Trump alternative that has the most momentum" owes, in part, to the first three GOP debates. She gave performances that were widely well-received, including by likely primary voters who responded to a series of 538/Washington Post/Ipsos polls. (DeSantis got high marks in those post-debate polls, too.)

"There's lots of historical precedent for how these debates can change the trajectory of a race. And at this point, I think she's shown that she's got the ability to perform under pressure," Kochel said.

New Hampshire Gov. Chris Sununu, a popular anti-Trump Republican, has been one of the major public advocates for finding an alternative nominee, pledging to campaign aggressively in his home state for someone besides the former president.

Speaking with ABC News' Rachel Scott outside of a standing-room-only Haley town hall in Hooksett, New Hampshire, last week, Sununu said his coveted endorsement was down to "the three governors" in the race: Haley, DeSantis and former New Jersey Gov. Chris Christie, adding that he would declare his support in the "next few weeks."

For her part, Haley, a former Trump ally and ambassador in his administration, has struck a delicate balance in her criticism of him as she works to build a coalition made up, in part, of his supporters.

At her Hooksett town hall with Sununu, she called Trump the "right president at the right time" while also saying he was an agent of chaos who attracted it -- "rightly or wrongly" -- and that it was time for the country to move on.

"When we've got an economy out of control and we've got wars around the world, we can't afford any more chaos," she declared to applause from the crowd.

The message seems to have resonated with some voters in the state. According to a November CNN/University of New Hampshire poll, Haley's support grew by eight points to 20%, trailed by Christie -- a harsh Trump critic -- in third and DeSantis a distant fourth.

While Trump led Haley by 22 points, a testament to his staying power, 53% of voters in the state expressed support for a candidate besides him.

In Iowa, a similar scene is playing out, with Haley jockeying for second place alongside DeSantis while Trump still leads by double digits. And though she has also seen her polling rise in her home state of South Carolina, where she is a comfortable second, Trump is the clear favorite.

If the current early polling bears out, he will easily win all three states -- and, likely, the party's nomination.

According to Kochel, the key to toppling the former president will be beating him in Iowa or New Hampshire, where he is polling slightly below 50%, to weaken the "air of inevitability" he's created.

"I think both of their goals, DeSantis' goal and Haley's goal, is to try and get the race situated where you go one-on-one into South Carolina and Super Tuesday and actually compete with Trump," he said, referring to the day in March when numerous states hold simultaneous primaries.

Janice Wood, a former Trump supporter from Portsmouth, New Hampshire, told ABC News in September she would cast her ballot for Haley after attending one of her town halls. She said that Haley's message that "it's time for something new" resonated with her.

"She's probably right about that," Wood said.

Haley has also drawn the backing of an entourage of potentially crucial megadonors, including Keith Rabois, who once called himself a "significant supporter" of DeSantis, and three of Sen. Tim Scott's largest donors after Scott bowed out of the race.

Republican megadonor Ken Griffin, who gave millions to DeSantis' 2022 gubernatorial campaign, said earlier this month that he was "actively contemplating" throwing his support behind Haley and was "at the finish line on that choice."

Sources familiar with Griffin's thinking told ABC News in July that the Citadel CEO had become frustrated with DeSantis' early campaign performance and later said publicly in September that he was remaining "on the sidelines" of the primary for the time being.

Haley's perceived strength has prompted the DeSantis campaign apparatus to go on the offensive, seeking to reclaim lost ground amid stagnating poll numbers.

Haley shot back on X, saying that none of DeSantis' ads "will erase the fact that he is losing momentum."

But he remains a formidable foe in Iowa, where neither candidate is a clear second.

DeSantis has established critical allies in the state, including Gov. Kim Reynolds and the influential evangelical leader Bob Vander Plaats, who leads the Christian advocacy group The Family Leader.

"He has a lot of upside potential in Iowa," Kochel, who has advised on strategy in the state for past presidential candidates like Jeb Bush and Mitt Romney, said of DeSantis. "And even though she's got some national momentum and momentum in Iowa, see how the next 60 days play out."

Haley's standing in Iowa was recently encapsulated in a moment with Marlys Popma, a long-time local GOP operative that some politicos have described as one of the state's most effective caucus organizers.

Rising during a Haley town hall in Newton in mid-November, Popma, who twice led the state Republican Party and The Family Leader, said while she walked into the event as an undecided voter, she was not leaving as one.

"I just wanted to tell Nikki I wholeheartedly support you. And I want to tell the people in this room this all happens in Iowa. And don't look at the polls. Don't look at what the media is telling you. Look at what you've heard today," she said, encouraging attendees to support Haley.

Thanking her for the endorsement, Haley said that "the number of people that are joining us and the momentum that we have is real."

ABC News' Soo Rin Kim and Will Steakin contributed to this report.