A major Democratic donor also weighed in, telling The Hill of Biden, "A lot of people are nervous that he's lost some of his mojo. They're getting nervous about him going toe to toe with Trump. But the problem is, there doesn't seem to be an alternative."
The report comes while Biden is on vacation for a week in his home state of Delaware.
Biden has a reputation for speaking his mind, but his mistakes on the campaign trail have become more frequent in the news of late. Over the weekend, the Democratic front-runner claimed he was vice president during the Parkland tragedy, which happened more than a year after he left office.
Last week, he slipped up and said "poor kids are just as bright and talented as white kids," before attempting to correct himself, and during his final statement at the last Democratic primary debate, Biden fumbled his words while trying to direct supporters on how to contact his campaign.
As far as his campaign goes, aides say Biden will stay the course as he always has.
"Joe Biden has spoken his mind his entire life, which voters know and love about him," said Biden's deputy campaign manager, Kate Bedingfield. "He's a real person, he's authentic, and that will never change. He's going to keep taking on Trump and making the case to voters about the stakes we face in this election, regardless of how the press chooses to cover him."