The Democratic debate between former Vice President Joe Biden Joe BidenSenate Republicans face tough decision on replacing Ginsburg What Senate Republicans have said about election-year Supreme Court vacancies Biden says Ginsburg successor should be picked by candidate who wins on Nov. 3 MORE and Sen. Bernie Sanders Bernie SandersKenosha will be a good bellwether in 2020 Biden's fiscal program: What is the likely market impact? McConnell accuses Democrats of sowing division by 'downplaying progress' on election security MORE (I-Vt.) was watched by a total of 9.9 million viewers on CNN Sunday night, with an additional 844,000 viewers tuning into Univision, according to Nielsen Media Research.

The debate moderated by CNN's "State of the Union" anchor Jake Tapper Jacob (Jake) Paul TapperCNN slammed for soft questions during Biden town hall: 'The media is broken' Biden's team says he views election against Trump as 'Park Avenue vs. Scranton' The spin on Woodward's tapes reveals the hypocrisy of Democrats MORE and chief political correspondent Dana Bash Dana BashTrump says officials will investigate whether California is using 1619 Project in classrooms Veterans Affairs secretary defends Trump: 'I judge a man by his actions' GOP senator dismisses national intelligence director election security briefings: 'This is blown way out of proportion' MORE, and Univision political correspondent Ilia Calderón, was dominated by questions concerning the coronavirus pandemic gripping the country.

It also marked the first presidential debate since John Kennedy John Neely KennedyMORE squared off against Richard Nixon in 1960 where an audience wasn't present for the proceedings due to the coronavirus precautions.

ADVERTISEMENT

The last Democratic debate, which took place before Super Tuesday on Feb. 25, drew 15.3 million viewers on CBS.

Prior to that, the Feb. 18 Democratic debate from Las Vegas on NBC and MSNBC delivered a record for a Democratic debate, with 19.7 million viewers. The event marked the debate debut of former New York City mayor Michael Bloomberg Michael BloombergTop Democratic super PAC launches Florida ad blitz after Bloomberg donation The Hill's 12:30 Report - Presented by Facebook - Latest with the COVID-19 relief bill negotiations The Memo: 2020 is all about winning Florida MORE.

The most watched primary debate of all time occurred in 2015 for the GOP debate featuring then-candidate Donald Trump Donald John TrumpObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE in August of that year, which registered more than 24 million viewers on Fox News.

Voters go to the polls on Tuesday in four states: Florida, Illinois, Ohio and Arizona.

Two states, Louisiana and Georgia, further down the primary calendar have postponed their respective contests amid the spread of the coronavirus.