There is no “mechanism” and there’s no “who will win?” equation to plug numbers into. Trump has a clear chance of winning no matter who the Dem nominee is. At this moment, it seems best for Biden to stay the course simply because the chaos involved in replacing him would make losing more likely.
I’m putting things in numerical terms there, but I mean this is kind of the basic question I’m getting at. Do these worries translate to a loss of vote share? I’m genuinely unsure of whether they do, and if they do, whether staying the course makes winning less likely than flipping the table over.