A review of decades of Biden's past debate performances and interviews with former rivals and their advisers show that while Biden's debates rarely stand out for tactical brilliance or panache, they're consistently good enough. They were enough for him to win the primary and may be good enough for him to preserve his lead in a general election where polling has been virtually static for months.
"I don't remember a lot of debates in the primary where Joe Biden was deemed a winner. He still won the primary," said Lis Smith, a former top adviser to Pete Buttigieg's presidential campaign.
"What does a win look like for Biden now?" Smith asked. "A win for him looks like brushing off the Trump attacks, engaging only when necessary and using a moment that will maybe be the largest audience he’ll have to speak directly to the American people."
Over nearly half a century in politics, Biden has sparred with lions of the Senate, debated the best and brightest of his own party in more than two dozen presidential primary debates and faced off against Sarah Palin on one hand and Paul Ryan on the other in vice presidential debates.
"We're talking about a different universe here," Sen. Chris Van Hollen, D-Md., said of Trump, whom Biden will confront for the first time Tuesday in Cleveland. Van Hollen role-played Ryan in mock debate sessions to help Biden prepare for the 2012 debate.
"Those were the days when catching your opponent in a flip-flop or making untrue statements could be a debate moment," Van Hollen told NBC News. "It's a whole different ball game with Donald Trump because he is a serial liar. He makes up stuff as he goes."
While Biden's political obituary was written prematurely several times during the primary after gaffes and awkward moments, Beto O’Rourke said those moments didn't bother voters who feel like they know the former vice president almost personally.
"What makes Joe Biden so strong as a candidate, including on a debate stage, and why people love him, is he is who he is," said O'Rourke, the former Texas congressman who faced Biden twice during his presidential run. "He's not pulling any tricks and trying to do 'gotcha' stuff or trying to be cute. He’s just himself."
"It is very hard to get under his skin,” O’Rourke said. "The guy is just naturally optimistic and aspirational. Sometimes these attacks were warranted, sometimes they were downright petty. But they just rolled off him."
Sawyer Hackett, who studied Biden's past debates and adopted his cadences while playing the vice president in primary debate prep sessions for Julián Castro, said Biden's style connected with people who don't follow politics closely.
"Biden — more so than anybody on that stage — is able to, in one minute or less, give the top-line punchline and then pivot back to his record on that issue, talk about what the Obama-Biden administration did on it," Hackett said. "And he uses every single question in a debate to reinforce narratives about his own life."
His durability frustrated some rival campaigns, whose candidates earned more acclaim for their debate performances than Biden.
"The press declared Amy Klobuchar the winner of every debate, but Joe Biden came out ahead almost every time," said Tim Hogan, who was communications director for the Minnesota senator's campaign. "We got a boost out of those debates, particularly before the New Hampshire primary, but no one on that stage was able to knock Joe Biden out with a debate performance."
Biden allies are interested in seeing him draw a character contrast with Trump rather than attempting to eviscerate him, arguing that the way to win over what few undecided voters remain is to come across as an experienced and stable alternative to the president.
"I hope I don't get baited into getting into a brawl with this guy," Biden said during a virtual fundraiser earlier this month.
But Biden is, after all "a scrappy guy from Scranton," as Van Hollen put it, and a temper is sometimes hiding just beneath, under his famous aviator sunglasses.
After one of Biden's first outings in a presidential debate, during his 1988 White House run, Washington Post television critic Tom Shales wrote that Biden came across as "terrifying" and "as someone whose fuse is always lit."
A debate that year ended his campaign when he cribbed from a British politician for his closing remarks and was accused of plagiarism.
Twenty years later, when he was Barack Obama’s running mate, Democrats worried Biden would be too aggressive with the inexperienced Palin and stir sympathy for her. Palin drilled for hours to try to get up to speed, according to her memoir, "Going Rogue," and her debate coach warned her, "He has spent literally decades on the art of political talking."
Jason Sudeikis, portraying Biden in a "Saturday Night Live" parody of the debate, said his goal "was a simple one: to come up here and at no point seem like a condescending, egomaniacal bully." He succeeded and the debate ended up being largely unremarkable.
Four years later, Biden held nothing back against Ryan, Mitt Romney’s running mate.
"With all due respect, that's a bunch of malarkey. Not a single thing he said is accurate," Biden declared at one point, laughing.
Biden’s "antics," as Ryan called them in his 2014 memoir, "The Way Forward," were controversial at the time. Republicans complained that Biden was rude and domineering for interrupting his much younger opponent 82 times.
Still, Biden laced his attacks with laughter, smiles and back pats, calling Ryan "my friend" 13 times — "I love my friend here" — so the two seemed to have enough of a rapport that Ryan helpfully offered a translation when the moderator asked what Biden meant when he called Ryan's comments, "a bunch of stuff."
"It's Irish," Ryan quipped with a laugh of their shared heritage. "It is," Biden responded.
Biden is a creature of a bygone clubby Senate who has always treated debate partners, from Michael Dukakis 1988 to Sen. Bernie Sanders in 2020, as a worthy opponent deserving respect.
It's impossible to imagine Biden calling Trump, a man he clearly does not respect and has barely met, "my friend" and meaning it.
But the challenge of debating the president should not be underestimated, many said.
"Trump is an almost impossible target," said Ari Rabin-Havt, Sanders' former chief of staff and deputy campaign manager. "Debating Trump is like boxing like one of those squishy dolls. It's just going to lie at you and remold itself constantly."
Biden himself seems confident. Mostly.
"I think I know how to handle bullies," Biden said at the fundraiser. "We'll find out."