Good morning and welcome to On Politics, your guide to the day in national politics. I’m Lisa Lerer, your host, taking over the morning edition for our debate recap.

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It’s a good thing that last night’s debate wasn’t taking place in California, because both candidates would have been forced to violate new state guidelines to attend.

On Sunday afternoon, Gov. Gavin Newsom called for all residents 65 years and older to isolate themselves at home. Both Joe Biden, 77, and Bernie Sanders, 78, would have fallen into that category.

I mention that new rule as a way of underscoring how quickly and profoundly American life changed over the weekend, as the country grapples with the spread of the coronavirus.

Crises have a way of clarifying distinctions. In last night’s debate, we got a much sharper glimpse into how Mr. Biden and Mr. Sanders view the problems facing the country.

Both of the Democratic primary candidates dismissed President Trump’s approach as insufficient, embracing a much further-reaching government strategy to try to mitigate the health and economic impacts of the virus.

But the scope of their responses differed significantly. Mr. Biden focused on immediate solutions, saying he would call upon the military to help handle the situation and work to enact a “multi-multi-billion-dollar program.”

The virus, as he sees it, is a short-term problem that requires an American reckoning, but then life would return largely to normal.

“Regardless of whether my plan was in place or his, this is a crisis,” Mr. Biden said. “This is like we are being attacked from abroad. This is something that is of great consequence. This is like a war. And in a war, you do whatever is needed to be done to take care of your people.”

Mr. Sanders, meanwhile, sees the virus as a symptom of systemic problems in American society like income inequality, the power of big corporations and the demise of the working class. He offered a more structural critique, rooted in the virus.

“As a result of the virus here, the coronavirus,” he said, “what we have got to do also is understand the fragility of the economy and how unjust and unfair it is that so few have so much and so many have so little.”

Mr. Biden shot back: “People are looking for results, not a revolution. They want to deal with the results they need right now.”

The two-man, audience-free debate certainly led to a more substantive discussion. There was no playing to the crowd or moderators dwelling on candidates without a clear shot at the nomination (ahem, Michael Bloomberg). Mr. Biden and Mr. Sanders debated bankruptcy law, campaign finance, climate change, immigration, Social Security, the Iran deal, the Iraq war, abortion rights and foreign policy.

Mr. Sanders delivered a forceful performance, turning policy critiques into questions about Mr. Biden’s leadership and trustworthiness. Mr. Biden’s team appeared to expect a less aggressive approach from Mr. Sanders. Anita Dunn, a top Biden aide, later described her candidate’s debate performance as “graciously dealing with the kind of protester who often shows up at campaign events, on live television.”

But none of the disagreements were particularly new. Voters paying enough attention to understand the details of those policy-heavy spats had most likely already settled on a candidate and which side of the party’s ideological divide they favor.

In that way, this debate seemed unlikely to inspire the kind of fundamental shift that would be required for Mr. Sanders to win the nomination. (Of course, at a time when our daily lives feel so scrambled, it’s not out of the question that something surprising could happen with our politics.)

Whether or not Mr. Sanders defies the odds and captures the nomination, his worldview — and the energized wing of the Democratic Party that it represents — isn’t going away. And if Mr. Biden wants to win the general election, he needs to find a way to see Mr. Sanders less as a pesky protester and more as a key partner in his political coalition.

A few other moments worth noting:

• Paging Senators Amy Klobuchar, Kamala Harris, Elizabeth Warren and other would-be vice-presidential picks. The news out of this debate is that Mr. Biden committed outright to picking a female running mate. The push for a woman on the ticket escalated after Ms. Warren dropped out of the race. For all you veepstakes lovers, this declaration isn’t that surprising but it does narrow Mr. Biden’s list of possibilities.

• Beyond the shrunken field of candidates, debating in the time of coronavirus looks awfully different. The podiums were placed six feet apart, in line with recommendations from the Centers for Disease Control and Prevention for keeping a safe distance from others. Only a dozen people were physically present in the Washington television studio where the debate took place. Hand sanitizer was widely available, and the candidates greeted each other with a careful elbow bump.

• Even if the logistics were different, it’s nice to see a campaign event happening, as so many primary elections are getting postponed. Georgia and Louisiana have delayed their presidential primaries, and Wyoming has suspended its in-person Democratic caucus voting. Yesterday, we reported that New York officials are considering plans to postpone the state’s presidential primary election from April 28 to June 23.

• In an interview after the debate, Mr. Sanders suggested that holding primaries may not “make a lot of sense” right now. “I would hope governors listen to the public health experts,” he said. “I’m thinking about some of the elderly people sitting behind the desks, registering people, all that stuff. It does not make a lot of sense.”

Photo of the day

Podiums were cleaned before the start of the Democratic debate on Sunday. The debate was moved from a theater in Phoenix to a CNN television studio in Washington because of concerns about the coronavirus.

Want more debate coverage?

• Here’s the recap that’s on the front page of the newspaper: On matters beyond the virus, the two men clashed over their divergent policy agendas and records in office.

• The coronavirus crisis brought Mr. Biden and Mr. Sanders together for an unusual debate, and the debate highlighted their distance, our news analysis says.

• We also have articles on Mr. Biden’s pledge to select a woman as his running mate, the candidates’ clash over Social Security, and their strategies to stay safe from the pandemic.

• So, how well did Mr. Biden and Mr. Sanders perform in the debate? Campaign experts weighed in on the candidates’ first one-on-one clash, and we rounded up their reactions.

• We fact-checked the candidates’ claims on topics including the coronavirus response, their health care plans, super PACs, the Green New Deal, immigration and the auto bailout.

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