NOT cool.
You do not do this to the flag of the United States of America. You do not turn the symbol of the country into a campaign flyer, even if U.S. Flag Code did not specifically prohibit it. Just because you're speaking for the "Office of the President-Elect" (whatever that is), YOU are not the symbol of the country. What's next? Everyone has to have a picture of "Dear Leader" in their homes? I don't think so.
Of course, this from the same guy who put the fake Presidential Seal up on his podium before he'd even gotten the nomination so I suppose it's not a surprise. This man is a narcissist, at best, and an incorrigible megalomaniac at worst.
(Photo from the Baltimore Sun.)