What's deplorable is that so many European members of NATO don't pay their fair share as promised and expect American taxpayers to make up the difference.
Where are you getting that idea?
Why should we spend our money defending you when you care little to defend yourself?
You are defending yourself. We have no illusions that you care about Europe as an advanced warning post (even if you should).
Europe's part of the NATO 'coalition' has agreed to increase it's level of military spending, up to 2% of GDP, and is on track. The USA has been sending mixed signals instead. Europe does challenge the rigid (old-style USA) framework since drones and cyber warfare have been developing.
Europe (i.e. The Netherlands) has penetrated Iranian nuclear sites (allowing the USA to plant a Stuxnet virus) and has penetrated Russian troll factories (hijacking their on-location webcams). Keep pissing off European partners, instead of joining forces, and we'll start focusing on merely our own interests.