In the television interview, Mr. Sanders also acknowledged his delegate deficit coming off a month in which Mr. Biden swept many large states, before the coronavirus crisis ground campaigning to a halt, leading a number of states to delay their primary contests.

“We’re about 300 delegates behind; Biden has 1200, we have 900,” Mr. Sanders said. “There is a path. It is admittedly a narrow path. But I would tell you, Seth, that there are a lot of people who are supporting me. We have a strong grass-roots movement who believe that we have got to stay in, in order to continue the fight.”

In an interview with MSNBC’s Brian Williams on Tuesday, Mr. Biden was asked to address that remark. He noted Mr. Sanders’s “very, very strong and ardent followers” and said the decision was up to the senator. But he added: “I feel confident about being the nominee. I don’t see much that’s going to make it, be able to change that.”

“We’ve been talking to Bernie’s people,” he went on. “I have respect for them. And I think there ought to be a way we could accommodate his concerns on other matters in terms of everything from people being engaged, to his organization. I think there’s a lot of things that can be done, but that’s a decision for Bernie to make.”

Earlier, Mr. Sanders also argued that the outbreak of the coronavirus crystallized the need for his sweeping single-payer health care proposal, “Medicare for all.” He said the crisis highlighted how vulnerable many Americans were without insurance and showed how the current public health system is “so weak, so incredibly weak,” that doctors and nurses don’t have access to basic protective equipment.