Republican presidential candidate Donald Trump campaigns in Milford, N.H., on Tuesday night. He is leading the polls in the state. (John Tully/For the Washington Post)

Donald Trump returns to the Republican presidential debate stage here Saturday night facing a crucible. Marco Rubio arrives as a sudden star, basking in the establishment’s embrace but fending off ferocious attacks from his rivals.

Still glowing from his Iowa victory, Ted Cruz is laboring to further consolidate conservative support, while Ben Carson is struggling to avoid being typecast as the dead man walking — or, in this case, talking.

Then there are the three governors, clumped together in the second tier. Without a breakout moment in Saturday’s ABC News debate to propel a surge in Tuesday’s New Hampshire primary, the candidacies of Jeb Bush, Chris Christie and John Kasich could end.

Beneath a blanket of snow that fell here Friday, the GOP candidates burrowed in to prepare for their most urgent debate yet, one that will influence New Hampshire’s famously late-to-decide voters and help determine the finalists in the nomination battle.

“People are voting, so there will be more desperation by everybody,” Christie, the New Jersey governor, said in an interview. “New Hampshire folks are going to be watching and deciding, and I will put on a good show for them.”

Dominick Rubio, 7, joins his father, Sen. Marco Rubio (R-Fla.), on stage during a campaign town hall event Thursday in Salem, N.H. (Chip Somodevilla/Getty Images)

The debate will put an exclamation point on two exhaustive weeks of campaigning and comes at a time when candidates like Christie are clawing to hang on.

Since Monday’s Iowa caucuses, state polls here have shown Trump maintaining a solid lead but Rubio and Cruz rising into contention, with Kasich and Bush close behind and Christie and Carson trailing. The eighth major candidate, former technology executive Carly Fiorina, did not qualify for the debate because she is too far back in the polls.

One-third of likely Republican voters here said they could change their minds before Tuesday, according to a Suffolk University-Boston Globe poll released Friday. The survey had Trump leading at 29 percent, followed by Rubio at 19 percent and Kasich at 13 percent.

The establishment candidates who looked past their poor results in Iowa see New Hampshire as the first — and perhaps last — meaningful test of their appeal.

Bush, the former Florida governor who was an early favorite but has languished through the fall and winter, is on a crucial mission to stage a comeback. He pleaded this week with New Hampshire voters to rally behind him.

For Bush and the other two governors, it is imperative to slow or stop Rubio, who had a strong third-place finish in Iowa. Bush has suggested that Rubio and Cruz, while ambitious and gifted, lack the experience and leadership qualities to be president, a refrain he is likely to carry into the debate.

Sen. Ted Cruz (R-Tex.) speaks to potential supporters at a meet-and-greet event Thursday at Generals Sports Bar and Grill in Weare, N.H. (Jabin Botsford/The Washington Post)

“What in their background would suggest that they can make a tough decision, that they’d run to the fire to put it out, that they’d figure out a way to solve problems because they’ve been confronted with challenges in their life?” Bush asked at an event Thursday in Derry.

Christie has been more scathing in his critique of Rubio. All week, he has called Rubio “the boy in the bubble.” In the interview, Christie described the senator from Florida as weak and callow.

“You all decided that he’s now all of a sudden become the anointed one,” Christie said. But, he asked, “what’s Marco Rubio’s major accomplishment in his political career?”

Asked whether he would press this attack in the debate, Christie replied, “If I get the chance to, I may.”

Rubio, 44, has sought to shrug off the criticism as he has glided from diners to packed town hall meetings delivering his message of generational change.

“I’m proud of my record in public service,” Rubio said Friday on NBC News, citing his years in the Senate and as Florida’s state House speaker. “People running say all kinds of things. . . . At the end of the day, this election is about the future, about what happens next for America.”

Cruz and Carson’s fates hinge less on the outcome in New Hampshire. They are playing more to a national conservative audience, looking ahead to the South Carolina primary and beyond.

By taking on Trump, Cruz, a senator from Texas, is looking to solidify his status as the darling of the hard right, while Carson, a retired neurosurgeon, is striving for relevance after shedding about 50 staffers this week.

Typically a low-key presence, Carson has grown angry this week about Cruz’s campaign in Iowa, which Carson accused of playing “dirty tricks” for claiming before the caucuses that he was suspending his campaign. Cruz has since apologized, but Carson does not plan to back off at the debate.

“He is still concerned about the culture of that campaign,” Carson adviser Deana Bass said Friday. “It’s not a talking point. It’s how this man truly feels.”

For Trump, who skipped last week’s debate in Iowa because of a feud with Fox News Channel, much is on the line.

“The man who has led it all for six months is in the most vulnerable position among the big three,” said former George W. Bush press secretary Ari Fleischer. “If having lost Iowa he also loses New Hampshire, it’s going to diminish him.”

Trump’s debate performances have been uneven, and if he does poorly Saturday night he will have little time to recover before voters render their verdict.

Taking to Twitter on Friday, Trump promised an “incredible evening,” with “so many things to say, so much at stake.”

On the stump this week, Trump has slightly recalibrated his pitch, reviving his core themes of border enforcement and trade and taking fewer shots at others. But signaling a line of attack the candidate may pursue Saturday, Trump adviser Stephen Miller excoriated Rubio’s immigration position in an interview with Breitbart News on Friday, calling him a “front man for the open-borders syndicate.”

One candidate who plans to avoid clashes is Kasich, the Ohio governor, who says he is campaigning from the “sunny side of the street.”

In an interview this week aboard his campaign bus, Kasich said he thinks he can grow his support if he avoids a fight.

“People keep thinking you’ve got to throw some Hail Mary pass to shake things up, but I don’t buy that,” he said.

He then shouted for his strategist, John Weaver, to join the conversation, and the governor declared proudly that he has not even come up with a zinger.

“Weaver!” Kasich said. “What do you think?”

Weaver nodded and said the goal for him — for everyone — is simply to “weather the storm.”