There are dems who want to replace him (Gavin Newsome so desperately) but no one with a possible future will risk taking him on.
Biden approval ratings are low now: https://www.reuters.com/graphics/USA-BIDEN/POLL/nmopagnqapa/
A non Trump R is going to win back states Trump lost in 2020 (GA, AZ). They have to win in MI, WI, PA etc. Will be hard but Trump did it in 2016.