The 11th Democratic presidential debate took place as the nation confronts the coronavirus pandemic, with the candidates' podiums set six feet apart serving as a reminder of the global public health emergency.
It was the first one-on-one showdown between the primary's two finalists. The delegate math suggests their race is approaching its end, with the former vice president building a clear lead that's expected to grow Tuesday with primaries in Arizona, Florida, Illinois and Ohio. But Sunday night showed that how the end occurs remains an open question.
Sanders repeatedly laid into Biden's record on Social Security and bankruptcy legislation, trade and more. But Biden -- who appeared to accept midway through that the two wouldn't find much common ground -- also decided to directly engage with Sanders on his record as well.
He also had an ace in the hole. Biden said for the first time he would pick a female vice president -- a significant development that Sanders didn't quite match.
Here are five takeaways from Sunday night's debate:
Coronavirus response: Results vs. revolution
The vast gulf between Sanders and Biden on politics and policy, as well as how they would approach the presidency, was on display in their responses to the coronavirus pandemic.
Biden sought to offer competency and showcase a detailed understanding of the federal government. He also touted his own experience, pointing to decisions he made during his eight years as vice president.
"This is like a war, and in a war you do whatever is needed to be done to take care of your people," Biden said, adding later that he would use the US military to respond.
Sanders, by comparison, argued the spread of the coronavirus was something that has exacerbated -- and even highlighted -- the flaws in the current US health care and economic system, casting himself as offering the wholesale change that he feels the country needs.
The Vermont senator also channeled the anger about Trump's leadership during this crisis.
"First thing we have got to do, whether or not I'm president, is to shut this president up right now," Sanders said, echoing other Democrats as he knocked Trump for "undermining the doctors and the scientists" who are leading the response.
The clearest illustration of their vast differences came in an exchange over economic inequality and the response to the coronavirus. Biden pledged to make people "whole," but offered a more focused approach on tackling the issue, while Sanders disagreed, saying it is "not good enough not to be understanding how we got here and where we want to go into the future."
"People are looking for results," Biden said, "not a revolution."
Biden pledges to pick a female running mate
Biden calmly dropped the biggest news of the night into an answer on protecting women's rights: He would pick a woman to be his running mate if he wins the Democratic nomination.
"There are a number of women qualified to be president tomorrow. I would pick a woman to be my vice president," Biden said.
CNN's Dana Bash followed up with Biden, asking point blank if he would pick a woman as his running mate. "Yes," he said.
The announcement has huge implications. Biden is currently the delegate leader in the Democratic primary and the odds-on favorite to be the party's nominee. His commitment could end up becoming reality.
Biden has long said he wants someone "simpatico" on policy as his running mate. He has also at times named a number of women as potential vice presidential nominees. He has singled out California Sen. Kamala Harris, former Georgia gubernatorial candidate Stacey Abrams, Minnesota Sen. Amy Klobuchar, Massachusetts Sen. Elizabeth Warren, former deputy attorney general Sally Yates and New Hampshire Sens. Maggie Hassan and Jeanne Shaheen.
Sanders was less committal about the idea of having a woman running mate.
"In all likelihood, I will," Sanders said. "For me, it's not just nominating a woman. It is making sure that we have a progressive woman and there are progressive women out there. So, my very strong tendency is to move in that direction."
The nation has only ever had two women vice presidential candidates: Geraldine Ferraro ran as Walter Mondale's running mate in 1984 and Sarah Palin ran as John McCain's running mate in 2008.
'I agree with Bernie'
Biden tried to extend olive branches to Sanders and his supporters Sunday night -- though his rival wasn't ready to bridge their ideological divides.
The former vice president pointed to his moves within the previous two days to embrace free public university tuition for those whose families make less than $125,000 per year and to embrace Massachusetts Sen. Elizabeth Warren's proposal to undo much of a bankruptcy bill they'd fought over 15 years earlier.
"I agree with Bernie," Biden said as they discussed surging help to hospitals facing the coronavirus pandemic.
"I agreed with Bernie," he said later when noting they both believed those on Wall Street responsible for the 2008 financial crisis should have gone to jail.
Sanders mostly didn't reciprocate, which a frustrated Biden pointed out.
"He's making it hard for me right now. I've been trying to give him credit for things and he won't even take the credit," Biden said.
Still, the former vice president sought to minimize his differences with Sanders in a bid to create an open door for the Vermont senator's supporters to migrate to Biden's campaign if he wins the Democratic nomination. Though Sanders disagreed, Biden said the two have the same priorities on health care, student debt, education and climate change.
"We disagree on the detail of how we do it, but we don't disagree on the principle. We fundamentally disagree with this president on everything," Biden said.
After a debate in which Biden touted Sanders-backed policies he's embracing, Biden's campaign made clear it views Sanders himself as an annoyance to be batted away. Senior Biden adviser Anita Dunn said Biden "for two hours graciously dealt with the kind of protester who often shows up at campaign events."
Can Biden win? 'I have my doubts'
Sanders, meanwhile, directly questioned whether Biden can defeat President Trump in the general election.
Sanders pointed to his strong support from young voters and Latinos. He also nodded to exit polls showing his own proposals on issues like Medicare for All being more popular among Democratic primary voters than Biden's positions, even as Biden has overwhelmingly won most states.
"I have my doubts about how you win a general election against Trump, who will be a very, very tough opponent, unless you have energy, excitement, the largest voter turnout in history," Sanders said.
"I have my doubts that Vice President Biden's campaign can generate that energy and excitement and that voter turnout," he added.
Sanders starts a policy brawl
Sanders arrived Sunday night ready to lay into Biden over votes he'd cast and comments he'd made over decades, casting the former vice president as too moderate for the modern Democratic Party.
They clashed over climate change, free trade, same-sex marriage and more. But the most illustrative battle was over Social Security, with Sanders bringing an attack that's been a fixture in his campaign ads into a debate.
"I am saying that you have been on the floor of the Senate time and time again, touting the need to cut Social Security, Medicare and veterans' programs," the Vermont senator said to Biden.
"That is not true," Biden shot back.
Sanders told those watching at home to visit YouTube -- where the first search result for "Joe Biden Social Security" is a video posted by Sanders' campaign in which Biden says to "put all of it on the table."
Biden said he was willing to put changes to Social Security on the table "in order to get the kinds of changes we need on other things related."
"But we did not cut it," Biden said.
"I know," Sanders shot back, "because people like me helped stop that."