Joseph R. Biden Jr. swept the three states that voted Tuesday: Florida, Illinois and Arizona. Bernie Sanders lost ground badly in the delegate count. And the coronavirus pandemic continued to wreak havoc on the most basic facets of American life, threatening to disrupt if not derail the remaining primary calendar.

With nearly 60 percent of the delegates allocated in the race for the Democratic presidential nomination, Mr. Biden holds a commanding lead of nearly 300 delegates over Mr. Sanders — a sum that makes it statistically improbable that Mr. Sanders could ever catch up.

“Is this race over?” Representative Hakeem Jeffries of New York, the House Democratic caucus chairman, asked on Twitter Tuesday night.

In a sign of his diminished standing, Mr. Sanders did not even try to spin the results for the second straight week, choosing to make no public remarks after the states were called.