Mr. Biden has just 32,000 subscribers on the influential video platform, a pittance compared with some of his rivals in the Democratic primary race and roughly 300,000 fewer than President Trump. The videos that Mr. Biden posts — these days, mostly repurposed campaign ads and TV-style interviews filmed from the makeshift studio in his basement — rarely crack 10,000 views. And the virtual crickets that greet many of his appearances have become a source of worry for some Democrats, who see his sluggish performance online as a bad omen for his electoral chances in November.

“This video is 2 days old and it’s sitting at 20,000 views,” one commenter wrote under a recent video of Mr. Biden’s. “This is a guy that is supposed to beat Trump?”…

The shift has been clumsy for Mr. Biden, an old-school retail politician who relishes face-to-face interactions. He lacks the social media firepower of Mr. Trump, whose 106 million combined followers on Facebook and Twitter dwarf Mr. Biden’s 6.7 million, and whose White House coronavirus briefings have allowed him to commandeer the news cycle. Mr. Biden’s first virtual town hall last month was marred by technical problems, and some of his other digital experiments — like a soporific campaign podcast, “Here’s the Deal,” which did not rank among the top 100 podcasts on Apple Podcasts as of this week — have not gone as well as hoped.