I'll admit, I didn't watch the debate yesterday and merely gauged everyone's reactions from social media, but maybe this is the point.

A lot if people don't pay attention closely, and so they will gauge an impression of Biden based on what others say of him. Speaking positively of him paints a good picture in those people's minds and therefore will cause other people to think higher of him.

Second thing is, it makes him look weak. We all care about democracy but many other people don't think too much about policy, but will want a leader they can feel proud of. A face of America. If they see one man's supporters turning up to rallies, celebrating him, borderline worshipping him, and another guy's biggest supporters (democrats) calling him weak/old, telling him to step down, saying he's the best of two bad options, saying he's immoral, that he's "just some old white guy"... what are they gonna think? They're gonna think even his own people don't like him and they can't see him being a fit leader. Even though he is. (People he works with saying he's a genuinely kind, strong leader, and the bare facts that he's benefited the American economy).

Politics is ultimately a game and, like Joe, the public image we create matters as it paints an idea in people's minds. Republicans understand this really well, which is why even after Trump's stupidest blunders, incoherent rambling and downright racist remarks, they have only ever celebrated him. Never faltered or kicked him while he's down. They've lifted him up constantly which is partly why this clown got elected in the first place.

I'm not saying Biden should have a similar cult-like following, but if people perceive others as supporting him then they will automatically see him as someone worthy of support and overlook A LOT in response to that (Trump proves this). The way we speak about him is a part of that brand. "At least he's not Trump" seems quite negative, and so does repeating all the attacks the MAGA people make against him. "He's a doer not a talker, and he has been doing an amazing job at leading our country" (a comment I saw on instagram) could be a more positive spin.