Biden also won Michigan, Mississippi, Missouri, and Idaho; Sanders won North Dakota. No woman has ever been elected as the US president or vice president, with Hillary Clinton losing to Trump in 2016 and two vice-presidential candidates falling short in 2008 and 1984.
The big picture: Biden was also the victor of Michigan, Mississippi, Idaho and Missouri on Tuesday - snatching most of the delegates up for grabs from Sanders, who faces a quickly narrowing path to the Democratic nomination.
Biden tops polling by significant margins in battlegrounds Arizona, Florida, Illinois and OH, where the 77-year-old former vice president could strike a hammer blow against his rival by building an insurmountable lead in the delegate count.
Neither Biden nor Sanders returned to the question of a death toll in the millions, nor did their media questioners ask them to do so, or ask how such a catastrophe could be avoided.
Symone Sanders, a senior adviser, said that Biden's main qualifications for his vice-presidential running mate are for someone who is simpatico with him, as well as someone that he works along with well. Biden said his plans for more measured improvements on top of the health care plan adopted under Obama - popularly known as Obamacare - would help more Americans at less cost.
"People are looking for results, not a revolution", Biden said during Sunday's debate, referring to Sanders' call for radical socio-economic change.
Neither candidate discussed whether workers should remain on the job under conditions where the best practice from the standpoint of public health is "social distancing", not cramming people into workplaces where they run a greater danger of contracting the infection.
Biden at one point cut off Sanders, saying: "With all due respect to Medicare for All, you have a single-payer system in Italy". Biden has large leads in the polls in all four states, although it was unclear who would actually turn out to vote under conditions of the coronavirus crisis. "It is making sure we have a progressive woman, and there are progressive women out there, so my very strong tendency is to move in that direction". Biden retorted, "It kept us from going into a depression".
Sanders claimed Biden supported cuts in the country's cherished Social Security payments to older Americans. View more opinion at CNN.
Biden needs a majority of at least 1,991 delegates at the convention and now leads Sanders, 809-666.