The night began under the shadow of the coronavirus pandemic. The two men bumped elbows rather than shaking hands, before taking podiums separated by extra space.
But it did not take long for the event to be transformed into a fairly standard political battle over the competing policy plans of two men representing opposing sides of a fractious Democratic Party. Biden and Sanders, united in going after their mutual enemy President Donald Trump, clashed on the typical array of party flash points.
Biden challenged Sanders over the price tag of "Medicare for All." Sanders said Biden had advocated for cuts to Social Security. In the night's biggest moment, Biden, who during the last debate held in South Carolina pledged to nominate a black woman to the Supreme Court, committed during Sunday's event that his vice president would be a woman.
All in all, at the end of two hours of debate, the state of the race was similar to when the night began.
Biden, ahead in delegates, is likely to be named the Democratic nominee to take on Trump unless something dramatic changes about the state of the race. Sanders, ideologically to his left, gave no sign that he intended to give up that prize without a fight.
Both Biden and Sanders cast themselves as better equipped to combat the coronavirus pandemic wreaking havoc on the United States than Trump.
After a day in which Trump downplayed the spreading crisis and said the U.S. has it "under control," the Vermont senator said "the first thing we've got to do is shut this president up" so doctors can do their jobs.
"It is unacceptable for him to be blabbering with unfactual information," he said.
Biden was asked about Trump saying Friday that "I don't take responsibility at all" for slow coronavirus testing and limited availability. He pointed to unspecified "rules" and "regulations."
The former vice president shook his head in disgust when asked about the president's comment. He faulted Trump for turning down the World Health Organization's test and instead insisting the U.S. develop its own.
A 2020 Democratic presidential debate could not pass without some disagreement on "Medicare for All." Sanders has called his single-payer health insurance proposal essential to making sure all Americans can afford testing and care during the coronavirus pandemic.
Biden pointed to Italy, where coronavirus has severely stressed the medical system, as evidence that government-run insurance would not help.
"It has nothing to do with Medicare for All. That does not solve the problem at all," he said.
Sanders countered by saying the U.S. does not have a "system that is prepared to provide health care to all people."
In making his case against Sanders' plan, Biden highlighted the House-passed legislation that would make coronavirus testing free for all Americans, including those who lack insurance. The senator said the bill has "enormous loopholes."
Pressed on whether they'd pursue industry bailouts to help American businesses recover from the COVID-19 pandemic, Biden and Sanders resuscitated their debate from the last financial crisis.
"We need to stabilize the economy, but we can't repeat what we did in 2008," Sanders said. "Joe voted for that, I voted against it."
Biden and Barack Obama, then a senator, supported the 2008 bailout packaged signed by President George W. Bush, which involved government purchases of $700 billion in toxic bank assets to rescue the economy.
Biden argued that the bank bail out was necessary to stave off financial ruin for millions of Americans.
"Had those banks gone under, all those people Bernie says he cares about would be in deep trouble. Deep, deep trouble. All those little people," he said.
Biden said he agreed with Sanders that " somebody should have gone to jail" but said that without the rescue package, the U.S. would've ended up in a repeat of the Great Depression.
"How do you get out of that? Bernie is saying that I guess he's going to do a wealth tax or something, that the top 1% could pay for everything, and they should pay for everything that occurred," Biden said. "We are talking about tens and hundreds of billions of dollars. That's what this was about. And the fact was that it saved the economy from going into a depression."
Biden whipped out some campaign statistics on Sunday to defend against attacks from Sanders and his allies over the funding behind his bid.
"The idea, Bernie's implication, somehow I'm being funded by millionaires," Biden said, after noting that the average contribution to his campaign was $51 this month and $44 for the entire campaign. He added: "Bernie outspent me two-, three-, four-, five-, six-to-one. And I still won! I didn't have any money and I still won."
Sanders fired back that Biden had condemned super PACs in the past, and called on him to do the same during the debate.
"Why don't you get rid of the Super PAC that you have right now which is running very, ugly, negative ads about me," Sanders said. "Don't laugh Joe, it's the truth. And they've got two other super PACs running ads against us. Why don't you just say right now on television — You know what, I think in the past Joe, if I'm not mistaken, you've condemned Super PACs, that correct?"
That prompted Biden to call on Sanders to get rid of "the nine super PACs that you have."
"I don't have nine super PACs. I don't have any super PACs," Sanders said.
"You have nine. Do you want me to list them?" Biden said.
"Yeah, you go ahead and list them," Sanders responded.
"Come on, give me a break," Biden said, although he did not list them.
"I commit that I will in fact pick a woman to be vice president," Biden said.
When moderators questioned whether that was a guarantee, Biden said "yes."
Sanders was less firm. When he was asked whether he would name a woman to be his vice president, Sanders said: "In all likelihood, I will."
Political analysts have named potential choices such as Sen. Kamala Harris, Sen. Amy Klobuchar, Sen. Elizabeth Warren, former Georgia state house lawmaker Stacey Abrams and Michigan Gov. Gretchen Whitmer.
Warren, Harris and Klobuchar were previously rivals of Biden and Sanders' in the primary race. They both endorsed Biden after picking up key primary victories and overtaking Sanders in the delegate count. Warren has yet to make an endorsement.