DES MOINES — Vermont Sen. Bernie Sanders — who has reignited his presidential campaign in the weeks since a heart attack put his political future in doubt — is now making a direct and sharpened case against former vice president Joe Biden in the final stretch before next month's Iowa caucuses.

In an interview between events here this week, Sanders said Biden’s record and ties to the political establishment make him ill-suited to defeat Trump in November — and urged Democrats to value voters’ appetite for sweeping change over Biden’s perceived electability.

“It’s just a lot of baggage that Joe takes into a campaign, which isn’t going to create energy and excitement,” Sanders said. “He brings into this campaign a record which is so weak that it just cannot create the kind of excitement and energy that is going to be needed to defeat Donald Trump.”

To understand how Bernie Sanders became a presidential contender, you have to start in Vermont. (The Washington Post)

Sanders’s focus on Biden comes as Sanders has recalibrated his efforts in Iowa, where the Feb. 3 caucuses will be a make-or-break moment for many campaigns.

Not long ago, few party strategists predicted Sanders stood much of a chance, with attention instead on Biden’s enduring stature atop the national polls, the surprising rise of former South Bend, Ind., mayor Pete Buttigieg and Massachusetts Sen. Elizabeth Warren’s appeal among the party’s liberal base.

But the 78-year-old senator has rolled out a new approach. He favors town halls over the raucous rallies that defined his 2016 campaign, there is a little less talk of revolution, there is far more engagement with minority voters and, everywhere he goes, a persistent emphasis on voters’ anxiety about escalating health-care costs.

The power of Sanders’s movement was made clear Thursday, when his campaign announced it had raised $34.5 million in the final quarter of the year, significantly more than his rivals. Biden announced Thursday that his campaign had raised $22.7 million in the final quarter, while Buttigieg earlier had said he raised $24.7 million. Warren has not announced her total, but it was expected to be notably lower than that of Sanders.

In the world of campaign fundraising, a single dollar is more important than you might think. The Post's Michelle Ye Hee Lee explains why. (The Washington Post)

The Sanders campaign also announced earlier this week that it has received more than 5 million individual donations, giving him a well of support he can tap again as he moves ahead.

A November poll from the Des Moines Register showed Buttigieg surging to a lead in Iowa but included a sign of durable and unwavering strength for Sanders: 57 percent of likely Democratic caucusgoers who say he is their first choice say their mind is made up. No other candidate in the field received more than 30 percent commitment from their top supporters.

If Sanders can pull off a win in Iowa, his team believes he would storm to the New Hampshire primary with a burst of momentum, then carry that to Super Tuesday, where his campaign has made the California primary a priority.

Positioning the Vermont independent for a possible long and bruising race against Biden has become increasingly central to Sanders’s planning, in part because his advisers see a fight for many of the same voters.

“When you think about it, Warren and Buttigieg are kind of going after that wine cave, kind of limousine Democrat — and they’re there, kind of important to the whole party,” said Pete D’Alessandro, Sanders’s senior adviser in Iowa. “We’re going to want them when we win the nomination . . . but a lot of working-class folks like Joe Biden. Joe Biden and the Bernie Sanders campaign are talking to a lot of the same people.”

In the interview, Sanders said Biden’s past backing of military intervention in Iraq would hurt him with young voters, while his support of free trade, including the North American Free Trade Agreement, would make him vulnerable in the industrial Midwest, where Trump scored victories in 2016.

“It doesn’t take much imagination to understand that Trump will be saying, ‘You see this guy? He voted for NAFTA,’ ” Sanders said.

Sanders also cast Biden as part of the political elite, cozy with Wall Street and unable to confront major financial institutions because of his record, such as his support for the bank bailout in 2008.

“People are tired of the traditional types of campaigns in which candidates like Joe are running to wealthy people’s homes and raising large sums of money,” Sanders said.

The Biden campaign declined to comment.

A Biden aide, who spoke on the condition of anonymity because the aide was not authorized to speak publicly, said of Sanders’s remarks, “There is nothing new here from Senator Sanders” and pointed to recent Mason-Dixon polls that show Biden running ahead of Trump in Florida and Virginia.

“That’s based on real data, not rhetoric or wishful thinking,” the aide said.

Tapping into health-care anxieties

As Sanders has toured Iowa this week, he has engaged in at times raw question-and-answer exchanges on health care that have shown how that issue galvanizes his core voters.

At a town hall in West Des Moines on Monday morning, Sanders turned to the topic almost immediately.

“What are you paying for in premiums? Does anyone want to volunteer? Don’t be shy,” he said.

Sanders called on Sheila Campbell, 51, an office manager at a medical clinic, who said her family is paying nearly $2,000 a month for health care. Then Laura Miller, 30, who was holding her 9-month-old son. She said she is “still paying hospital bills for him.”

“You’re still paying off the birth of that baby?” Sanders asked, his voice hoarse and incredulous. “Help me out here. Your quote-unquote illness is that you had a baby? Is that your illness?” She nodded.

Sanders kept up the back-and-forth on health care for about 15 minutes, one painful anecdote after another, followed by his fury and, finally, applause when he called for a revamp of the whole system.

Stoking support among minority voters by targeting health care is also critical. Sanders spoke to Latino voters Sunday night, as his campaign served Puerto Rican platters. He has visited mosques and Muslim community centers in Iowa and met with African American and Native American leaders.

Although Iowa’s electorate is 90 percent white, Sanders’s campaign sees an opening for engagement with the other 10 percent, which includes thousands of working-class minorities who have never caucused.

Sanders said in the interview that drawing people out about their health-care challenges is essential to his strategy in Iowa and elsewhere — giving voice to people’s anger. It is an effort steeped in bleak stories, but one he believes has power.

“What you see, what you hear — it would bring you to tears,” Sanders said.

“Hundreds of thousands of people are seeing this” on social media, he continued. “They’re saying, ‘You know what? She isn’t the only one hurting, who can’t afford health care. He isn’t the only one working for 10 bucks an hour.’ People go, ‘Oh, I thought I was the only person! Turns out I’m not.’ ”

Unlike Warren, Sanders has declined to specify how much it would cost to implement his Medicare-for-all plan.

“I don’t give a number and I’ll tell you why: It’s such a huge number and it’s so complicated that if I gave a number you and 50 other people would go through it and say, ‘Oh . . .” he said, his voice trailing off.

“What I appreciate more now than I did four years ago is the cruelty of the system,” Sanders said. “Last time I talked about health care as a human right … but what I see now is the cost of health care.”

Doubters in the crowds

Skeptics are plentiful, even among some who come to Sanders’s events. They wonder if an avowed Democratic socialist who had a heart attack in October can win.

“I know how I feel at this age, which makes me wonder about him,” Mary Walkup, 68, said in Winterset, Iowa. “I want to hear him out, but I do wonder if we should look to someone younger.”

Deborah Hansen, a 69-year-old retired educator at that same town hall, said she shares many of Sanders’s grievances but would find it hard to go door to door in her town and announce herself as his supporter because she still feels uneasy about how Sanders handled his defeat in the 2016 primary race.

“It’s hard for me to get over the feeling that he didn’t do enough to help Hillary,” Hansen said. “I like him, but I also like Amy Klobuchar,” the Minnesota senator who has campaigned heavily in Iowa, “since I really don’t want to see Trump win.”

There are also questions about the viability of his huge proposals to overhaul the way government works, from Medicare-for-all to eliminating the nation’s student debt and offering free college tuition.

At the West Des Moines town hall Monday, a Sanders supporter who works at a private college gently asked him if his own job would be in jeopardy if Sanders’s plans were enacted. Sanders assured him that was not his intention and said he would put a “great deal of emphasis on expanding Pell grants” that could go toward funding study at private schools.

Former Ohio governor Ted Strickland, a Biden supporter, said this week that Sanders “should not be discounted” and “seems to be less of a grouchy old man since he came back from his heart condition.” But he warned Democrats to resist him and dismissed the suggestion that Sanders would have a better chance against Trump in a November faceoff.

“My big concern isn’t that he’ll beat Joe, but that this movement of his may decide to take a walk if Bernie isn’t the nominee,” Strickland said. “It’d be deadly to the Democratic Party if he didn’t do everything he could to support the nominee.”

Sanders said in the interview, “I will support someone if they’re more conservative than me because I think it’s imperative that we beat Trump.” But he also made clear that, even if he stumbles, he has no plans to drop out until the race is over, saying what he is “certainly prepared to do is contest every state in this country.”

When asked if he would make overtures to moderate Democrats should he win the nomination, Sanders said the party would have to adjust to his movement rather than the other way around.

“People in the Democratic Party are going to take a look at reality and in a millisecond, they’re going to make a decision: The choice is between Bernie Sanders and Donald Trump. They may say, ‘Oh, God, I don’t like Bernie Sanders. . . . He doesn’t comb his hair nicely enough. But you know what? There is no choice. We’re going to support Bernie Sanders.’ ”

Trump, who occasionally tweets about “Crazy Bernie,” has kept an eye on Sanders for months, according to a White House official who spoke on the condition of anonymity because the official was not authorized to speak publicly — as have senior Republicans, many of whom see the senator as beatable.

“Many Republicans would see a Sanders nomination the same way Conservatives in the United Kingdom used to talk about the Labour Party’s move to the left in 1983: the longest suicide note in political history,” said Steve Schmidt, a veteran consultant who worked as a strategist for the late John McCain’s 2008 presidential campaign. “They’d run against him as a radical who once traveled to the Soviet Union and ask, ‘Do you want to give up one of the greatest economies ever for that?’ ”

Sanders fiercely rejected that view and says Democrats must rally around his movement in order to beat Trump, rather than assume that Biden might have a better chance of winning.

“Trump will be a formidable opponent,” Sanders said, because of his “strong base of support,” “the fact that he’s a pathological liar” and “because much of the billionaire class will be supporting him.” In addition, Sanders said he suspects Trump may break the law and use “federal agencies to help” his bid.

“The way you defeat Donald Trump is by having the largest voter turnout in the modern history of this country — that’s how you beat him,” Sanders said. “We think we can get 5, 10, 15 percent of the vote Trump got because an increasing number of people who voted for Trump understand now that he’s a liar and fraud” who backed conservative policies.

The night before, Sanders held a New Year’s Eve party at the Marriott in downtown Des Moines, which was a proudly informal affair. Those in tuxedos seemed to do so in jest, and most Sanders advisers wore jeans and T-shirts as they mingled with more than 1,000 supporters. New Power Generation, the late Prince’s former backup band, tore through covers.

Members of the media sat in the back in the dark, ignored by the Sanders crowd amid the revelry. Attendees toasted “the Bern” and spoke excitedly about the prospect of victory in February. The bitter disappointments of four years ago seemed distant.

Hours before midnight, Sanders took the stage and told them to believe.

“I have no doubt — no doubt that with your support, we’re going to win here in Iowa!” Sanders shouted, whipping up the crowd as he rattled through a list of future contests.

“We are in this struggle together,” he said.

The crowd roared. They were in.

And on that night, at least, no one wanted to wonder if that was enough.