Yes. It was essentially his entire argument for the nomination in 2020. The fact that he went from "the only one who can beat Trump" to "the only one who can lose to Trump" is already very damaging.
Who, besides Biden, in your view could beat Trump?
Personally, I only know of one other who could do it. A lady who ran in 2016.
Booker would’ve won. Klobuchar too. Senator Bennett or Jay Inslee. Maybe even Warren, who would’ve curb stomped Trump in that debate.
I don’t think Bernie would just because he’s too far left for the general. Really I wish neither Biden nor Bernie had run. We’d be in a totally different race right now. Biden is good at getting legislation passed but is a thoroughly uninspiring and ineffectual leader.