He doesn’t do what normal U.S. presidents do and make unequivocal statements about solidarity against shared threats. He asks them to pay up.
Rhetorically at least, he seldom distinguishes between allies and adversaries. And when he does, he often saves the toughest words for America’s allies.
Trump’s theory of the case is that Europe needs us more than we need them. And certainly for now, at least, Europeans have nowhere else to turn for their protection.
It’s possible his theory works out in the long term and they become militarily much more self-sufficient. But what’s not clear is what it will mean for the U.S. in the long run to draw down so much goodwill with our traditional allies.