Voluntary weakness isn't the same as structural weakness. Change the conditions, remove security guarantees, add security challenges from both Russia and America, and with sufficient prodding, Europe will wake up. It will take some time, decades, and at first Europe will concentrate on being able to defend itself without help, rather than being able to project power to other continents. But Europe has nuclear missiles, and enough population, money, industry, and science to grow its military significantly. Europe is weak out of a belief that military strength isn't terribly useful anymore; shattering that belief will probably have unintended consequences. European powers were global superpowers for centuries, and that was with them fighting each other constantly. External threats could accelerate European unification / collaboration and remilitarization to a point where it would easily surpass Russia, and rival the US and China as a global superpower. Europe is weak because its military spending as percentage of GDP is small; raise that to 1938 levels, and Europe is suddenly bristling with guns.

The Trump administration despises Europe, and hates international treaties. To me that suggests they don't understand what a treaty like NATO actually was made for, and how much it actually favors the US who dictated those treaties. Turning Europe from their most loyal ally into their rival isn't going to make America great again. If anything, it diminishes American capacity to project power globally.