I prefer that my presidents don't draw red lines in the sand unless they defend them. Leave yourself an out if you don't intend to make good on a promise. Voice it as a strong possibility, not a promise of action.
But, Trump is neither a politician nor a lawyer, and he makes no effort to parse his words. He talks like a Michigan line worker. That's why this is a problem at the international political level...but it is also why he has support at the voter level.