WASHINGTON – Former vice president Joe Biden pledged Sunday to appoint a woman as his running mate if he wins the Democratic nomination, and Sen. Bernie Sanders, I-Vt., said he would likely make the same decision as they met in an extraordinary two-man debate conducted under circumscribed conditions to guard against the growing coronavirus pandemic.

“There are a number of women who are qualified to be president tomorrow. I would pick a woman to be my vice president,” Biden said, in what was the first debate of the 2020 primary race that did not have a woman onstage.

Sanders stopped just short of a similar commitment. “In all likelihood I will,” he said. “For me it’s not just nominating a woman. It is making sure that we have a progressive woman – and we have progressive women out there.”

The pledges came midway through a debate that began with calls for national unity in the face of a historic medical crisis but soon descended into a testy policy-based battle over who had the best credentials and leadership record to lead the Democratic Party.

The first 40 minutes of the debate were dedicated to the coronavirus crisis, with Biden repeatedly suggesting that a leader other than President Donald Trump would have taken actions to slow the spread of the virus, while Sanders said the pandemic has been worsened by the lack of a single-payer health care system.

Both candidates support federal subsidies for testing and treatment of the new virus. Sanders told Americans that those who become ill should seek immediate treatment and feel assured that their bills would be paid for by the government.

“This is bigger than any one of us,” Biden announced at the start. “This calls for a national rallying.”

Far more time was spent re-litigating decades of legislative disagreements between the two men as they battled over the practicality of their plans, their liberal credentials and who had created a bigger political movement. The debate lacked any game-changing moment, with Biden having a steady performance that is likely to soothe his supporters and with Sanders continuing to aggressively press him on policy issues.

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

The candidates also once again jousted over the expansive Medicare-for-all health-care program that Sanders has proposed. He said that the current crisis has exposed the “dysfunctionality” of the current health care system and that everyone should have coverage and not have to worry about going to the doctor or paying for potential costs.

That triggered a rebuttal from Biden, who said other countries have similar programs right now and are no better prepared for the global pandemic.

“With all due respect to Medicare-for-all, you have a single-payer system in Italy,” Biden said, referring to its devastation by the spreading virus. “It doesn’t work there. . . . That would not solve the problem at all.”

“We are at war with a virus,” Biden continued. “This has nothing to do with co-pays or anything.”

Both candidates repeatedly criticized the Trump administration’s handling of the crisis and said that the United States should be moving much more aggressively and working more closely with other countries. They took aim at what they see as a lack of leadership by Trump.

“The first thing we have got to do, whether or not I’m president, is to shut this president up right now, because he is undermining the doctors and the scientists who are trying to help the American people,” Sanders said. “It is unacceptable for him to be blabbering with unfactual information, which is confusing the general public.”

The first one-on-one debate of the cycle allowed the candidates to talk for long stretches, and the moderators gave them time for a lengthy back-and-forth without interruption. But the debate also was somewhat subdued; the lack of a studio audience meant no interruptions from cheering supporters. The candidates also seemed mindful of broader concerns in the nation, though that did not entirely preclude some punching.

Sanders repeatedly challenged Biden on his role in the passage of the Bankruptcy Abuse Prevention and Consumer Protection Act of 2005 and voting for the Hyde Amendment, which blocked federal Medicaid funding for abortion services.

“I voted against it in the House, and I was right,” Sanders said about the bankruptcy bill. “And I don’t have to rethink my position, because that’s what leadership is about, having the guts to take an unpopular vote.”

Biden announced last week that he would support revisions to the bankruptcy bill that have been proposed by Sen. Elizabeth Warren, D-Mass. “The bankruptcy bill was going to pass overwhelmingly, and I improved it,” Biden said about his 2005 vote. “I did not like the bill. I did not support the bill, and I made clear to industry that I did not like the bill.”

The first matchup since Biden seized control of the race – winning at least 15 of the last 21 states in one of the most dramatic comebacks in recent political history – was the most significant debate-stage test he has faced and a crucial indicator of whether Sanders could change the course of a race that has been slipping from his grasp.

Both candidates faced political challenges, with Biden hoping not to alienate Sanders supporters who have long been wary of him but make up a potent force in the party, and with Sanders at risk of being criticized for damaging the more-likely nominee the way he did in 2016, when his attacks on Hillary Clinton had lasting damage.

Biden joked about his attempts to reach out to Sanders supporters. “He’s making it hard for me right now,” Biden said. “I was trying to give him credit for things; he won’t even take the credit!”

The debate was unusual from the start, coming in the middle of one of the most significant public health crises in the nation’s history. The candidate podiums were placed six feet apart, in accordance with Centers for Disease Control and Prevention guidelines for social distancing during the novel coronavirus outbreak, and the debate had been moved from a theater in Phoenix to the CNN studios in Washington so the candidates wouldn’t have to travel as far.

As the two candidates took the stage, they bumped elbows instead of shaking hands, and then stood silently. Each said later that he was hewing to guidelines that all Americans have been asked by health officials to follow.

It was thought to be the first presidential debate without a live audience since 1960, when John F. Kennedy faced Richard Nixon in a television studio.

It took place after an extraordinary week, one that reoriented daily American life as the nation grapples with the global pandemic and the presidential campaigns struggle to adjust as well. As the candidates met, there were 3,244 confirmed cases of the coronavirus in the United States and 62 recorded deaths from the disease, according to the Coronavirus Resource Center at the Johns Hopkins University school of medicine.

Biden, 78, and Sanders, 79, both said Friday that they had not been tested for the virus, with each saying he is showing no symptoms and has not been in contact with anyone he knows who has tested positive. Both, along with Trump, are in an age cohort deemed most at risk if they contract the virus.

Campaign workers for Biden and Sanders have been instructed to work out of their homes; the candidates have dropped all pretense of a normal campaign and are scheduling virtual events instead of in-person ones. Anthony Fauci, the head of the National Institute of Allergy and Infectious Diseases, said Sunday morning that it would be “several weeks to a few months” before daily life returned to normal, complicating the remaining primary calendar.

Georgia and Louisiana have delayed their primary election days to May and June, respectively. Four states are set to hold primaries Tuesday – Arizona, Florida, Illinois and Ohio. Secretaries of state from those states said in a joint statement Friday that they have no plans to delay.

Biden has made recent efforts to reach out to Sanders’ supporters, beginning the process of trying to unite the party and bring under his wing a faction of it that has been deeply distrustful of him. In the hours before the debate, Biden said he will adopt a version of Sanders’ proposal of making public colleges and universities free, though the Biden plan would apply only to families who make $125,000 or less, compared with Sanders’ plan to offer the benefit to all Americans.

Sanders had forecast some of his attacks last week, listing a range of issues that he thought Biden was on the wrong side of, before ending with the mantra, “Joe, what are you going to do?”

The most heated and personal exchange came when Sanders criticized Biden for his past willingness to cut Social Security. Biden denied saying that there should be cuts to entitlement programs, triggering an outburst form Sanders.

“All right America!” he said, arms spread wide. “Go to the YouTube right now!” He pointed to numerous clips of Biden having argued that everything was on the table, including cuts to programs such as Social Security. Biden argued that he was willing to put the potential cuts on the table as part of a broader deal.

“But we did not cut it,” Biden said.

“I know,” Sanders said. “Because people like me helped stop that.”

The candidates also had a vigorous exchange over the role of money in politics, with Sanders saying Biden was relying on wealthy donors to fund his campaign.

That triggered Biden to point out that he has been heavily outspent by Sanders, yet has been able to rack up victories on a shoestring campaign.

“I didn’t have any money,” Biden said. “And I still won!”