Hillary would not have left the 9/11 ceremony unless she absolutely had to. She has always made 9/11 her signature issue and, amid concerns about her health, she would not have left unless she had no alternative.
As she got into her car, she appeared to faint, losing a shoe as she was virtually carried into the car.
She won't withdraw unless he has to. But anxious Democrats will be so worried if she fails to be able to campaign and her health escalates as an issue that they might bring unbearable pressure on her to step aside.
If that happened, the Party rules state that the Democratic National Committee -- two from each state -- would be empowered to nominate a new presidential candidate. Tim Kaine would have no special claim on the nomination and, if there were a switch in the presidential nominee, would remain as the VP candidate.
Democrats are getting more and more nervous about Hillary's campaign now that she has blown her August lead and settled into a tie with Trump. If she is sidelined for much of the campaign, their worry is likely to reach a crescendo.
In any event Hillary will now be forced to release her medical records, a step she has heretofore resisted and perhaps submit to a new examination.
Be careful what you wish for. Biden would be a lot harder to beat than Hillary.