Don't be so certain. I bet all the committed Dems will vote the Dems ticket regardless of who is on it. The simple truth is that trump is a divisive figure and arouses strong dislike (TDS). Most of it is due to biased media coverage but not all of it. He just rubs some people the wrong way.That sucks.
Without knowing who the replacement would be it adds uncertainty to November. Leave the turnip in there and it's a Trump train runaway.