Dont under estimate europe on this. Yes USA has a lot of clout within Nato but they are also reliant on the other countries for their input. If you take the numbers of troops available to Nato without the USA Nato can muster more. There is no way Trump can risk a fighting war with a Nato alliance.
However Europe does need to remove reliance on American hardware, planes etc. It will do more in the long run to hit America in their pockets.