Only two Republicans, Nikki Haley and Ron DeSantis, will take the CNN debate stage at Drake University in Des Moines on Wednesday night for the final televised clash before the Iowa caucuses next week.

The man they are both chasing, Donald J. Trump, is yet again skipping any debate in which his front-runner status could be challenged in person, instead taking part in counterprogramming on a rival network, Fox News, with a prime-time town hall of his own.

It’s exactly the sort of split screen that Mr. Trump has sought throughout the cycle: his rivals bickering among themselves while he presses his case without meddlesome interruptions.

Here are five things to watch.

Nikki Haley wears a white hat and a pink jacket in cold weather as she looks to the left of the camera.
Nikki Haley has been fending off attacks from Gov. Ron DeSantis in Iowa, and Mr. Trump in New Hampshire.Credit…Hilary Swift for The New York Times

Ms. Haley has entered the final phase before the first voting of 2024 begins in Iowa on Monday as perhaps Mr. Trump’s most serious challenger, a status that, she likes to joke on the trail, has earned her lots of new attention from “the fellas.”

She is very much waging two wars at once.

One is a contest in Iowa against Mr. DeSantis, whom her allies have said she hopes to finish ahead of, in second place. The other is a race against Mr. Trump in New Hampshire, where some polling shows her gaining significant ground before the primary there on Jan. 23. She is within striking distance in some surveys, especially if support for Chris Christie, an anti-Trump candidate, were to flow to her.

But Ms. Haley has made blunders in the run-up to Iowa. She left out slavery when asked about the causes of the Civil War, and more recently said in New Hampshire that voters in the second early-voting state would “correct” those in the first.

“It was very condescending,” said Cody Hoefert, a former co-chairman of the Iowa Republican Party who is supporting Mr. DeSantis. “Like Iowa doesn’t matter, almost, and I think Iowa voters will hold her accountable for it.”

The DeSantis team certainly believes it’s a Haley line that will resonate. His campaign has announced its “closing TV ad” before the Iowa caucuses — and the spot opens with Ms. Haley’s correcting remark.

The fact that Mr. DeSantis, who for months spoke about the 2024 primary as a “two-man race,” is closing with an ad that starts by attacking Ms. Haley says a lot about how the primary has gone so far for him.

His predictions of finishing first in Iowa have morphed into a fierce fight with Ms. Haley. The debate on Wednesday is his best chance to seize late momentum, a dynamic that has historically been crucial in the caucuses.

The debate format — only two candidates will be on the stage for the first time — should give him ample opportunity to make his case, which increasingly has included that Ms. Haley is in the pockets of her contributors, some of whom flocked to her only after he had faded.

Mr. DeSantis is coming into the debate off the backs of two well-received voter town halls on CNN and Fox News, where he showed signs at both events of zeroing in on a closing message.

Mr. DeSantis has improved as the debate season has deepened and, unlike Ms. Haley, he has recent practice in a one-on-one contest — the unusual debate he held with Gov. Gavin Newsom of California in November, when he appeared particularly energized.

The question now: Will he bring the same spark to this showdown?

So about that two-front war.

Ms. Haley isn’t getting attacked just by Mr. DeSantis in Iowa but also by Mr. Trump in New Hampshire. The former president’s super PAC has started running a tough ad dredging up a line she used in 2015 in which she said those who were in America illegally were not “criminals.”

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“They’re families that want a better life, and they’re desperate to get here,” Ms. Haley said in 2015, in comments that the Trump operation has highlighted in conservative news media.

“Illegals are criminals, Nikki — that’s what ‘illegal’ means,” says the narrator in the new Trump super PAC ad.

As governor of South Carolina, Ms. Haley had signed legislation advertised as tough on immigration, but the party has drifted further right on the issue in the last decade.

Immigration and the border are top issues in the Republican primary. The narrator in Ms. Haley’s most recent ad says, “Your family deserves a border, secured.” So although the debate is in Iowa, her answers on immigration will also play in New Hampshire, where she is being blitzed with negative advertising on the topic.

Both Ms. Haley and Mr. DeSantis will be pressed by the two CNN moderators, Jake Tapper and Dana Bash, veteran political anchors who are likely to ask tough questions.

Donald Trump walks backstage between blue curtains, with American flags in the foreground.
Mr. Trump’s town hall appearance will be at the same time as Wednesday’s debate between Ms. Haley and Mr. DeSantis.Credit…Doug Mills/The New York Times

Mr. Trump has done three other town hall-style events with Fox News and Sean Hannity this election cycle. But even in those friendliest of settings, the former president can make unwelcome headlines. In December, Mr. Hannity tried to get him to brush aside talk of retribution or dictatorship.

“You are promising America tonight you would never abuse power as retribution against anybody?” Mr. Hannity said.

“Except for Day 1,” Mr. Trump replied. Mr. Hannity looked perplexed. “He’s going crazy,” Mr. Trump continued, referring to his host. “Except for Day 1.”

His Fox News town hall will be moderated by Bret Baier and Martha MacCallum, who oversaw the Haley and DeSantis town halls on Monday and Tuesday.

Mr. Trump’s goal is to avoid doing anything that could threaten his position as the front-runner in the race.

Gov. Ron DeSantis stands on a stage, holding a microphone and pointing with his finger as a seated audience looks on.
Mr. DeSantis has seen his grasp on second place slip as the primary process has wore on.Credit…Jordan Gale for The New York Times

Ms. Haley has found a line of attack on Mr. Trump that feels familiar to those who closely followed his 2016 run, when Jeb Bush tried to attack Mr. Trump as “the chaos candidate.”

The problem then was that voters seemed to want the chaos. Even Ms. Haley has said that in 2016, Mr. Trump was the right candidate at the right time.

But now, it’s Ms. Haley deploying the notion of chaos and hoping that the context — after four years of a Trump White House followed by three years of a Biden White House — means it will resonate differently.

“He was good at breaking things,” Ms. Haley said of Mr. Trump at her Fox News town hall on Monday. “Now we need somebody to fix them.”

Chaos, of course, is in part code for the four criminal cases and 91 felony counts that Mr. Trump is facing, and that most of his rivals, save for Mr. Christie, have treated gingerly.

Mr. DeSantis has a favorite new line, too, that he will most likely unfurl on the debate stage: Mr. Trump is running on his own issues, and Ms. Haley is running on her donors’ issues, but only Mr. DeSantis is running on the voters’ issues.

One of the questions heading into the final debate before the caucuses is whether Mr. DeSantis or Ms. Haley will take a more forceful approach to attacking the candidate they both badly trail, or will settle for scoring points only against one another.

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