He never said cut defense. In fact he has said our military has been weakened. What he is saying, and rightfully so, is we can no longer support and protect everyone. We are in debt 19 trillion. It makes no sense to continue at our expense to be the world’s bodyguard. Usually with little or no appreciation.
Japan is paying quite a bit, if not the most out of all of our allies for protection. I would prefer anything related to defense is the last part to be modified. I’m sure there are many other useless regions/nations (case in point, the entire continent of Africa) that is not of strategic importance that we can cut first.