Actually, I don't think he would have defeated her.
But if he (and we) assumed that he could NOT have defeated her--in a very BLUE state that is much more in-tune with his liberal leanings, where he is known best and very, VERY popular,,,,
WHY IN THE WORLD WOULD HE THINK HE COULD BEAT HER NATIONALLY,,,when 'flyover country' is much more conservative than a blue state like NY??