Here are five things to watch for in tonight’s debate.

Fewer candidates means less competition for time — which could make it easier for one candidate to break out and, at least potentially, be seen as Donald J. Trump’s main rival. (The former president, who skipped the two previous debates, will host a rally outside Miami as his rivals spar.) And the debate clock is ticking — right now, only one is scheduled, on December 6. in Tuscaloosa, Ala. – so the candidates will try to make the most of this television moment.

The changing landscape will most likely alter the strategic calculations of the candidates who qualified under the Republican National Committee’s rules: Nikki Haley, the former governor of South Carolina and former ambassador to the United Nations; Ron DeSantis, the governor of Florida; Chris Christie, the former governor of New Jersey; Vivek Ramaswamy, the entrepreneur; and South Carolina Senator Tim Scott.

Here are some things to keep an eye on during the two-hour debate that aired on NBC.

It’s Nikki Haley’s moment

Ms. Haley has attracted more attention in recent weeks as other candidates — most notably former Vice President Mike Pence — have lost support or dropped out. She has an opportunity to use her momentum to eclipse Mr. DeSantis, her biggest rival in the race, as the best Trump alternative.

“Haley is now the only candidate with a clear path to breakthrough against Trump,” said Mike Murphy, a longtime adviser to Republican presidential candidates who is not involved in this campaign. He said he expected the debate to be about “doubling down on her moment as the race heats up.”

Ms. Haley has a choice here: Will she spend more time attacking Mr. Trump or challenging Mr. DeSantis? Her campaign released a video Tuesday attacking the governor on energy policy, suggesting Mr. DeSantis should not expect an easy night.

Can DeSantis still play the frontrunner?

In the first two debates, Mr. DeSantis played the frontrunner, attacking his opponents only when he was hit first. That may no longer work as he faces mounting pressure to slow Ms. Haley’s rise in the polls and reassure voters who have come to question his political agility and strength as a general election candidate.

This has not been an easy period for Mr DeSantis, not least because of Mr Trump’s attacks on everything from his foreign policy credentials to his height. But Mr. DeSantis is on friendly terms in Miami: He was re-elected as governor last year after a defeat. And this week he received the support of Kim Reynolds, the governor of Iowa. Mr. DeSantis has staked his bid on his performance in the state’s first caucuses on Jan. 15.

But in a sign that Mr. DeSantis’ stature may be waning, Mr. Christie said he would likely largely ignore his rival tonight.

“What are you attacking?” he said in an interview. “If he says something that I think is worth responding to, I’ll respond to it. But I’ve been on the debate stage with him for four hours now, and I haven’t heard him say anything worth responding to yet.”

A world in turmoil

Foreign policy, with a few notable exceptions over the years, has proven inconclusive in the battle for the presidential nomination. But the war in Ukraine and bloodshed in the Middle East are likely to feature prominently in Wednesday’s debate.

The issue of U.S. aid to Ukraine has divided the Republican Party and could reveal clear differences between the candidates over whether they would follow Trump’s isolationist, populist path. Pressure will likely be on the candidates whether they support House Speaker Mike Johnson’s first major proposal: a plan to tie money for Ukraine to a border bill that is unpopular with Democrats.

Although the Republican Party is more united in its support of Israel (unlike the Democratic Party), the conflict has spawned some of the field’s sharpest criticisms of Mr. Trump.

At the meeting of the Republican Jewish Coalition last month, Ms. Haley, who has more foreign policy experience than her rivals on stage, attacked Mr. Trump for calling Hezbollah “very smart” and challenging Prime Minister Benjamin Netanyahu of Israel later described as weak. Hamas’ deadly attack on Israeli settlers.

Mr. DeSantis made a similar criticism of the president during his campaign in New Hampshire in October. “This is not the time to do what Donald Trump did by attacking Prime Minister Bibi Netanyahu, attacking Israel’s Defense Minister and somehow saying Hezbollah was ‘very smart’.” he said.

Does anyone else have a chance?

Of the three undercards, according to Republicans, Scott is the only one who seems to have a good chance of breaking through. So far, he has been swept away by higher profile opponents, and the likelihood that this debate will focus on Ms. Haley and Mr. DeSantis will not make things any easier.

Mr Ramaswamy proved to be an energetic debater in the first debate, but in the second debate he became increasingly a target. Since he’s polling in the single digits in many polls, he doesn’t loom as a major player in the race going into tonight. And Mr. Christie can hardly be more out of step with much of the Republican Party with his relentless attacks on Mr. Trump: He is routinely booed at Republican events.

Is there anyone?

An important question is how many people will watch at all. The number of viewers dropped from 12 million in the first debate to just under 10 million in the second debate. Unless Trump makes a dramatic appearance on stage at the last minute, it seems unlikely this will change.

The dwindling audience is perhaps no surprise given Trump’s dominance. With Trump comfortably ahead of the rest of the Republican field in most polls, the race may feel like it’s over before a single vote is cast — even though large swaths of Republicans have said they’re out least open to nominating anyone other than Mr. Trump.