[Read more: Bernie Sanders has officially ended his 2020 presidential campaign.]

Senator Bernie Sanders of Vermont was reassessing the future of his presidential bid on Wednesday after a crushing round of primary losses left him with no realistic path to the Democratic nomination and the 2020 race itself was on hold because of the coronavirus outbreak.

Mr. Sanders’s campaign has stopped actively advertising on Facebook, and his campaign manager sent an email to supporters without asking for donations — the kind of steps that sometimes precede the end of campaigns. His aides say Mr. Sanders is not suspending his bid, even as some Democrats have become increasingly vocal that he should consider leaving the race.

The party’s front-runner, Joseph R. Biden Jr., has now amassed a nearly insurmountable lead in delegates needed to clinch the nomination after winning the Arizona, Florida and Illinois primaries on Tuesday. Mr. Biden has swept so many states and attracted so many demographic groups that Mr. Sanders has little left to go on besides his political message and his passionate base of liberal supporters.

Some Democrats said that with the delegate outlook so bleak, and with a deadly pandemic gripping an anxious nation, Mr. Sanders risks appearing self-centered and out of step if he insists on pressing ahead.