Ryan Greenwood, director of movement politics for People’s Action

Mr. Greenwood’s group, a grass-roots organization that endorsed Mr. Sanders in December, emphasized how the current crisis revealed the serious vulnerabilities of the working class, a subject that Mr. Sanders has made central in the 2020 campaign.

The coronavirus pandemic means that almost everyone in the country is now feeling the crisis and instability faced by the multiracial working class on a daily basis. The question is, as Sanders has said, “Joe, what are you gonna do?” The choice is pretty simple: On one hand we have a platform where nothing fundamentally changes, in which we leave millions of people out of the solutions when crisis hits. On the other hand, we have a platform in which no one gets left behind, everyone’s well-being is protected, and everyone can pursue their full potential. We look forward to Sanders highlighting that contrast.

Evan Weber, political director of the Sunrise Movement

The Sunrise Movement, a group of young activists that has been instrumental in pushing the Green New Deal, endorsed Mr. Sanders in January. Mr. Weber emphasized that the Vermont senator still enjoyed a huge advantage among young voters, and that Mr. Biden must recognize that he needs to win over young people to win.

With questions of electability clearly shaping voters’ decisions in this election, Senator Sanders needs to use this debate as an opportunity to show Democratic voters why he’s the best candidate to take on Trump. Luckily, the senator has a clear case to make: No Democrat can win in November without the support and enthusiasm of young people, and millennials and Generation Z are swinging in wide margins for Bernie because he is championing a platform that meets the scale of our generation’s challenges.

Ana María Archila, co-executive director at the Center for Popular Democracy Action

Ms. Archila’s group, which supports Mr. Sanders, represents a number of smaller organizations that work with community groups on issues including immigration, health care and housing.

The coronavirus pandemic has exposed how fragile we all are when millions of people are uninsured, and when workers cannot afford to take a day off from work because they risk falling back on their bills. On Sunday, we hope to hear Senator Sanders not only make the case for these policies in the context of the current crisis, but also force Biden to commit clearly to the agenda that has mobilized young people. Throughout his campaign, Bernie has asked people to fight for someone they don’t know. We hope he will use this debate to remind people that we must take care of one another, and use our democracy to build a society where we all can thrive.

Maurice Mitchell, national director of the Working Families Party

The Working Families Party initially endorsed Senator Elizabeth Warren in the fall, but moved to support Mr. Sanders after Ms. Warren left the race.