The hard “floor” for Biden is probably at close to 40%. These are the Democrat “dead-enders” who will vote for a rotting roadkill possum carcass as long as there is a “D” after its name. So we’re getting pretty dang close to dead-ender-ville for him. And remember, this is with the MSM cheerleading for him! So the “dead-ender” line for Democrats is much higher for Democrats than it is for Republicans. My wild guess it that it at about 25-30% for Republicans.
But Biden is very clearly well into territory where even self-described (but non-shill) Democrats disapprove!