By nearly all objective analysis his path to “legitimate” victory is very narrow.
Is it possible? Yes.
Is it probable? No.
Is it even less probable than 2016? Absolutely.
Even then, “legitimate” is a word that covers all manner of sin like widespread voter suppression, election system tampering and destruction, intentional opposition voter harm, and welcoming foreign interference and manipulation.
If he stays in office it will much more likely be due to efforts to subvert the legitimate election results.