Besides the dementia stuff, the big reason it's so dangerous for Biden to debate Trump is that Trump can nail him to the wall by forcing him to denounce the extremists who set the Democrat agenda. Biden wants to pretend Abolish the Police was never a thing.
The classic "tack to the center" Dem move, which the antediluvian Biden is well versed in, relies upon disciplined left-wing extremists willing to shut up and let the Dem pretend to be "moderate" so they can win the election, knowing payoffs will come later.
That's not going to work now that lefties have been letting their freak flag fly, Biden is a doddering figurehead, and the big stars of the Dem Party are all raving left-wing loons. Personality cultists will not allow themselves to be disrespected.
The left-wing extremist movements aren't going to let themselves, or their righteous agendas, be minimized or disrespected. Trump can easily put Biden in one squirmy spot after another by quoting lefty superstars by name and demanding Biden denounce or marginalize them.
The GOP campaign must work hard to prevent the media from memory-holing these whack jobs. Biden claiming he wants to increase police funding is like a guy from Sinn Fein saying he's uncomfortable around explosives. Keep reminding the American people what the Dem agenda really is.
The Dem candidate can normally pretend the hard Left is a peripheral distraction to his moderate campaign, while the media helps the extremists submerge and load their torpedo tubes, but not this time. The Dem Party is primed to explode if the extremists feel disrespected. /end
