Clinton is already at threshold in continuing to press on with campaigning when she so obviously has medical problems, most notably her coughing fits, which are occurring more and more often, and more intensely.
If she keeps going the way she has, there's a good chance she could keel over at the podium in mid-sentence (recall that Joe Biden had to catch her a couple of weeks ago). Or she seizes, which we've also seen on occasion.
That, or she could start coughing up blood. That would be a lot harder to make jokes about.
That, or she could start coughing up blood.The news media will pretend it never happened.
What is going to happen tonight is the deck will be stacked. The questioners will be pre-selected victims of Trump's insults with gotcha questions for Trump. Hillary's questions will have been supplied by the DNC.