Trump stepped on it. He should have ignored the remark, or pointed out that “while no one is questioning John McCain’s military record, that has no bearing on [whatever]”.
Trump is an amateur.
Finally a correct statement by you! Congrats. Yes, Trump is not a professional politician. Trump is a businessman who as a rule will not give you rosy promises. It will all be straight forward words from his heart and mind. Frankly I am disappointed by the actions of professional politicians for 25 years.