Tonight, former vice president Joe Biden and Vermont senator Bernie Sanders will meet onstage to debate for the 11th time in the 2020 campaign season-but it's never been quite like this. We're days into a state of national emergency over the coronavirus pandemic that is rapidly spreading across the country. It's the first time the two men will face off one-on-one in a debate like this. And after spending months portrayed as an underdog, Biden is now the presumptive favorite to be the Democratic nominee for president.

Tonight's debate starts at 8 pm ET (5 pm PT), and is hosted by CNN and Univision.

The Democratic field has narrowed significantly since the last debate, which took place just before the South Carolina primary last month and saw seven candidates onstage. Then Biden won South Carolina in resounding fashion, and has kept up that momentum, taking a commanding delegate lead after Super Tuesday and continuing to win in key states like Michigan last week. Now every other candidate aside from Sanders and representative Tulsi Gabbard has dropped out of the race.

As of Sunday, in a surprise to no one, only Biden and Sanders qualified to participate in the debate, each having reached at least 20 percent of the total pledged delegates so far-the criteria decided by the Democratic National Committee. While Sanders lags behind Biden in the delegate count, 890 to 736, he said in a speech after Tuesday's primaries that he was staying in the race and looking forward to asking Biden some questions tonight.

The primary topic on everyone's mind these days, of course, is the novel coronavirus, and the US health care system's preparedness, or lack thereof. Not only is the pandemic dominating the news, it's directly impacting the race, from candidates canceling rallies to states like Louisiana and Georgia postponing their upcoming primaries. (The four states with primaries this Tuesday-Arizona, Illinois, Florida, and Ohio- have indicated that they will continue as planned.)

Sanders has defined his candidacy in large part on Medicare for All, his proposed solution to the dysfunctions of the health care system. Biden offers his own vision of post-Trump White House leadership that harkens back to the relative normalcy of the Obama era and his own vice-presidency, but it's nowhere near as transformative as Sanders' platform. For millions of Democratic voters, that moderation is key to Biden's appeal. For Sanders and his supporters, however, a return to the status quo still leaves too many Americans behind.

None of the debate organizers so far has mentioned focusing tonight's questions on health care and related topics alone. But maybe they should. Epidemics hold up a mirror to the societies in which they spread, and many Americans are facing historic disruption to their lives. One challenge facing the US right now is how to protect its most vulnerable: Who will get tested and who can afford treatment? Who can work from home or get paid sick leave, and who doesn't? Who might go hungry or lose housing? There is no better time for a serious discussion of the policies and choices that for millions of Americans are a matter of life and death.

Unlike the presidential debates, which are simulcast across all the major networks, primary debates-for either party-air on a rotating cast of news organizations. The 11th Democratic primary debate is being hosted by CNN and Univision, in partnership with CHC Bold PAC, which is associated with the Congressional Hispanic Caucus.

The debate was supposed to be held in Phoenix, Arizona, but on Thursday the DNC announced that out of an abundance of caution and to reduce travel, it would instead be held at CNN's studio in Washington, DC. There will also be no live audience.

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