Of course the US spends a larger portion of its GDP on defense than the other NATO members. NATO isn’t responsible for security in the Pacific or the Middle East.
Part of our enormous defense budget is attributable to soaring health care costs, which are less of a problem in Europe.
If Russia isn’t a real threat and NATO is consequently obsolete, as Trump has maintained in the past, what would be the point in the Europeans spending more money on defense?
Simply spending money without a well-defined purpose is stupid. If Trump can point to particular NATO functions that are dangerously underfunded because of the parsimony of the Europeans, complaining about free riding would make sense, but he doesn’t do that–he only talks about inputs, not outputs.
It would also make more sense for Trump to talk about burden sharing if he wanted to cut the defense budget and reduce costs to American taxpayers, but he doesn’t. He supported a big increase because it makes him feel more powerful, and he loves military parades. The Europeans aren’t going to subsidize that.