I guess it depends on what you mean by Democrats. There were some quite high ranked people openly critical and suggesting replacing him (more than I would expect). Dems are not a singular entity… but the only person with the power to replace the candidate at this point in time is Joe Biden himself. So if he doesn’t step down I do expect most high-ranked Dems to fall in line.
Here I think lies the main problem. When Biden was elected in 2020, in my understanding the goal was always for him to warm the seat for the next/younger generation. In those 4 years nobody stepped forward, and they are scared of proposing a forward looking vision because it may alienate some voters (either on the left or in the center). So now we have the choice between stagnation or actively tearing down Democracy.