Sununu was right. Obviously, for Trump's extremely online fanbase, Trump is super popular. But in reality he's been trounced by 2 popular votes. Clinton beat him by 3mil and Biden by 7mil. The horrible things he's done and said, and continues to do and say, have led to him being worshiped by some but has turned off permanently a lot of other people.
This is probably a big part of Biden's conundrum. He knows Trump is a loser. He knows, because he did it in a near-landslide, he can beat him. But he's also presumably aware of his aging, and certainly aware of the 24/7 thing going on against him. The best choice is probably to step away in favor of Harris but it's much easier to say that outside, than for him to make that choice himself.