But in years past, Biden has thrived in the one-on-one format during vice presidential debates. His plan Sunday is to focus on his electability and how he’s in sync with the Democratic electorate after winning 15 states, according to aides.

In the face of aggressive questioning from Sanders, Biden can now point to record turnout in states like Virginia, which overwhelmingly supported him. Then there’s the fact that he won nearly all of the African American support in Mississippi. What’s more, Biden has won whites by big margins and racked up wins in the cities, suburbs and in rural areas, a fact that advisers hope will give him a sense of confidence against Sanders.

“Success builds on success,” said Ron Klain, Biden’s top adviser in charge of debates.

In the first debate since Feb. 25 — four days before the South Carolina primary that transformed Biden’s candidacy from hospice patient to juggernaut — Biden is expected to be careful not to come across as too arrogant.

“The flip side is this thing, we’ve seen it change before, we’re taking nothing for granted,” Klain said. “I expect a lively contest on Sunday and a lively contest on Tuesday.”

Biden is prepared for Sanders to question his shortcomings with reaching out to the youth vote, and to acknowledge he needs to make gains with young voters. But the former vice president’s advisers say he’ll also note that Sanders fell short of his own promise that he had the singular ability to attract new voters and build a coalition that would beat Trump.

Biden is also expected to mention how most of the top former presidential candidates in the race endorsed him — and not Sanders.

Sanders, meanwhile, is operating under some self-imposed constraints. The Vermont senator likes Biden and loathes Trump, and he doesn’t want to eviscerate Biden out of concern that it would only weaken him and therefore help Trump, Sanders advisers say. And they note the difficulty of being overtly political onstage at a time when coronavirus dominates the nation’s consciousness.

Attacking Biden too much could be perceived as just out of step with the moment in which Democrats want unity and seriousness of purpose.

“Bernie’s going to be careful about not looking too political — too electoral — and being the guy who says, ‘Well, I can get this many delegates and go on to the convention...’ No. That’s not where Americans’ heads are at,” an adviser said. “People are worrying about their families. They’re at the grocery store buying batteries.”

Because coronavirus has made health care an even more important issue, Sanders is expected to press Biden on his opposition to Medicare for all. Sanders also wants Biden to explain why he advocated for cutting Social Security years ago only to inaccurately suggest he never did.

“It’s not going to be an all-out assault. It’s going to be a policy debate. And it’s going to be a vigorous one,” said Jeff Weaver, Sanders senior adviser. “But it’s going to be on policy.”

Klain said his candidate is ready for whatever Sanders throws at him.

“They have met on the debate stage 10 times already. I’m pretty sure I know what Bernie Sanders’ position is on Medicare for All and I know what Joe Biden’s position is on Medicare for All,” Klain said. “If people are expecting some big new thing on Sunday, I don’t think they’re going to get it.”

Klain, who served as Biden’s chief of staff while vice president, earned acclaim as the Obama administration’s czar who successfully managed response to the Ebola virus. Biden has tapped that expertise for his coronavirus response plan, and aides believe the issue is a strength at a moment when President Trump’s unsteady performance has generated criticism.

According to NPR, exit polls showed about half of Michigan voters said they believed Biden was best equipped to lead in a crisis to Sanders’ 31 percent. In Missouri, 61 percent said they trusted Biden to lead in a crisis to Sanders’ 26 percent. Advisers also say Biden would contrast his approach to Trump.

Biden, of course, has a well-earned reputation of going off-script, misspeaking or meandering. His first debate performance was arguably his worst. That’s when then-2020 rival Kamala Harris called him out for highlighting his ability to work with Southern segregationists in the 1970s and challenged him on busing policies. The debate went so badly, Biden felt compelled to address his performance at a Chicago event the next day.

“We all know that 30 seconds to 60 seconds in a debate can’t do justice to a lifetime commitment to civil rights,” Biden said.

Biden’s performances stabilized over time — or critics just became accustomed to his style — and he was praised recently for televised town halls in Nevada and South Carolina as well as the strength of his debates in both of those states.

What also helped Biden was billionaire Mike Bloomberg, a candidate who promised to save Democrats upon Biden’s collapse but instead delivered a disastrous performance in Nevada when Elizabeth Warren shredded him on stage, taking the focus off the then-struggling Biden.

Weaver said Biden has benefited from the big debate stages like that one in Las Vegas that have allowed him to avoid engaging in actual debate.

“With eight to 10 people onstage,” Weaver said, “it’s very difficult to have the kind of back-and-forth debate that voters need to make a good decision about who they want to pick as their nominee. That’s the problem.”

Last week, the two campaignsclashed over the debate format. Sanders campaign wanted a standing debate that was moderated by professionals. Biden’s campaign was more inclined for a seated town hall-style format where citizens could ask questions.

Biden has tended to thrive when given more time to argue a point or explain policy ideas. In town halls, potential voters at times would express relief at seeing Biden in person, saying hewas far more articulate and cogent than the candidate they’d seen on the debate stage.

Prior to this year’s crowded debates, Biden distinguished himself with several strong performances in vice presidential debates in 2008 and 2012.

“Joe Biden is simultaneously the most-experienced presidential campaign debater in modern American life but has the lowest expectations,” said Michael Steel, an adviser to former Rep. Paul Ryan before his 2012 vice-presidential debate with Biden, whose performance was credited with helping to reverse the fortunes of the Obama-Biden ticket.“We expected him to be over the top. We expected him to be blarney-full, if that’s a word. And he just took it to 11.”

The dispute with the Sanders campaign over the debate format came as Democrats sympathetic to Biden started privately raising concerns that Biden didn’t have the physical or mental stamina to face Sanders on stage. Rumors circulated that the Democratic National Committee was under pressure to cancel the debate, which both the DNC and Biden’s campaign denied.

The debate ultimately wasn’t canceled, but it wasmoved to Washington, D.C., from Phoenix over concerns about coronavirus contagion.

Mike Ceraso, a former adviser to Sanders’ 2016 campaign, said Biden has captured the feeling of the party better than his opponents, winning a different type of expectations game.

“Expectations this time around isn’t about brains or performance. It’s about the story, man. Pete and Warren and Bernie’s stories are okay,” Ceraso said. “Biden’s story hits home. Loss and anger and sense of service and sadness are relatable qualities. They amplify with Trump in the background. Take the intellectual out of it. And focus on the heart. It’s cliche as hell. But...imagine if you’re someone who has a mom with Alzheimer’s or a depressed child or someone addicted to drugs.”