Democratic candidates for president will have their second debate Saturday night.

Who: Hillary Clinton, Bernie Sanders and Martin O’Malley

Where: Drake University, Des Moines Iowa

When: 9 p.m. ET

Length: Two hours

How to watch: CBS will air the debate live and stream it via cbsnews.com/live/

Moderator: “Face the Nation” anchor John Dickerson

Panelists: CBS News Congressional Correspondent Nancy Cordes, KCCI anchor Kevin Cooney and Des Moines Register political columnist Kathie Obradovich

When the Democratic presidential candidates gather in Des Moines, Iowa, on Saturday night for their second debate, Bernie Sanders has a mission: Stop the bleeding in the key early voting state.

Sanders, the Vermont U.S. senator who went from insurgent long-shot to serious challenger over the summer has seen his numbers crater in three of the first four states to vote in 2016: Iowa, South Carolina and Nevada. Sanders remains competitive in New Hampshire, although most polls there have Clinton with a slim lead. Former Maryland Gov. Martin O’Malley is a distant third in all four states.

Saturday gives Sanders a chance to re-establish his campaign in a two-hour prime time debate. But, it could be too late, Rachel Paine Caufield, associate director of the Harkin Institute and a political science professor at Drake University, said.

“I’d say Bernie Sanders’ peak over the summer would be difficult to sustain,” Caufield said.

Caufield refuses to say that Sanders’ time has passed as history shows Sanders still has time to rally before the Feb. 1 caucuses.

In November 2003, former Vermont Gov. Howard Dean had a double-digit lead in Iowa, but ended up finishing third in the 2004 caucuses, behind both eventual nominee John Kerry and former North Carolina Sen. John Edwards. At this point in 2007, Hillary Clinton still led Barack Obama in Iowa polls, while Obama won the 2008 caucus by nearly 10 percentage points.

But neither Obama in 2008 nor Kerry in 2004 overcame deficits like the one Sanders now faces in Iowa. After catching Clinton in Iowa polls in mid-September, Sanders now trails by 20 to 30 percentage points, depending on the survey.

“We’ve seen this in a lot of other cycles where someone emerges early on as a challenger to the mainstream and kind of crests over the summer, late-summer, early fall and then, as more and more voters start to evaluate critical questions … the field starts to settle down,” Caufield said.

Quinn Symonds, of Mason City, Iowa, is the volunteer organizer of Iowans for Bernie, an unofficial support group. He said these final two-and-a-half months of the campaign are most crucial.

“The majority of people in Iowa haven’t even made their minds up yet,” Symonds said, referring to recent polling showing more than 50 percent of likely caucus-goers have yet to pick a candidate.

Plus, Symonds said, many who at first dismissed Sanders are reconsidering.

“A lot of people thought, ‘Oh, he’s going to be a protest candidate,’ and questioned his ability to even campaign,” Symonds said. “but, he has proven quite the contrary.”

Sanders has just as impressive an organization as Clinton does in Iowa, each with dozens of staffers and offices across the state. Sanders has proven, too, that he can raise enough money to be more than viable.

Sanders’ anti-corporate message of fixing the wage gap, punishing Wall Street scofflaws and protecting average Americans plays well in Iowa, Symonds said.

An example: Sanders has announced his opposition to a planned oil pipeline that would dissect Iowa from North Dakota to Illinois. More than 600 Iowans showed up Thursday for a state utilities board hearing on the Bakken Pipeline proposal.

Sanders’ opposition to the pipeline shows a firm grasp of Iowa-centric issues, Symonds said. “That’s a big reason why a lot of Iowans are excited about him, because not too many politicians, even state elected officials, have come out against it,” he said. “It ties right in to what he’s all about.”

Still, even if Sanders gains traction as fall turns to winter, he’s not running in a vacuum. Clinton is considered the front-runner for a reason. She has money, organization and history in the state that is more impressive than the University of Iowa football team’s 9-0 record.

Clinton’s campaign staff even talk like a big-time football coaches, many of whom publicly worry that the lowliest opponent is David to their Goliath.

“We have said from the beginning that we were going to fight like we were behind and that’s what we’ve done,” Clinton spokeswoman Christina Reynolds said. “We know things can change quickly.”

Clinton will use Saturday’s debate to focus on her message for the country.

“She is really proud of the policies she has laid out,” Reynolds said. “She took a lot of time in developing her prescription for the problems facing America and how she’s going to solve them and help American families.”

Penny Rosfjord, a Clinton supporter from Sioux City, Iowa, said the campaign cannot take solace in what happened in previous election cycles.

“I don’t look back,” Rosfjord said. “I only look forward.”

Rosfjord said Iowans have the same concerns as most Americans. They’re worried about the cost of college, about equal pay, school funding, jobs and access to health care.

“I think Hillary Clinton can do good things for the United States,” she said.