From your Webster's link, I think this definition should be noted as well:

Originally Posted By: Webster's
b : a persistent false psychotic belief regarding the self or persons or objects outside the self that is maintained despite indisputable evidence to the contrary


Emphasis added by me. Again, there is no indisputable evidence to contradict their belief that the election was stolen. Let me restate my position here: I agree with you that the election was probably a legitimate win for Obama, but I cannot concede the possibility that it wasn't, nor do I agree with your broad labeling of those who disagree with your view as delusional (but they probably are).

The only true way to test if they are delusional would be to present them with some indisputable evidence that the result was legit and see how they respond.