But Mr. Biden’s eventual announcement now seems fated to fall in the shadow of the recent allegations and the progressive concerns he has so far declined to address. Far from remaining above the fray, Mr. Biden will enter the campaign as bruised as any of the 16 other candidates already in the race.

“They’re in this never-never land right now,” said David Plouffe, the former strategist to President Barack Obama’s campaign, “because they’re being treated by the outside world like they’re in the race full speed and they’re not. That’s a really tough place to be.”…

Even some of his strongest allies are growing anxious. “I’d like to see him go ahead and get engaged because the summer is going to be here before you know it, the debates are going be here before you know it,” said Senator Doug Jones of Alabama, who was a state chairman for Mr. Biden’s 1988 presidential bid.