Beyond that, if you do get into the specifics of force projection (and basically anything logistical to do with NATO), you see that the entire alliance was built on the assumption that the US would contribute the capabilities that kept the whole system viable.

So,

    $(US) + $(ALLIES) > $(US) 

However,

    $(ALLIES) - $(US) < $(ALLIES) 

This has been true from the beginning, and I don't think was a nefarious plot, or even mistake, for most of the alliance's history. The further we get from the Cold War alignments within which NATO was created, however, the more difficult it has become to sustain.

'Keep the Russians out, the Americans in, and the Germans down' was a central tenet of NATO from its founding.

The problem is, this looks so much like a rerun of post WW1 America.

Tariffs (check - Smoot Hawley), American isolationism (check - America First), I guess we won't be far from the economic crisis (not checked yet - Great Depression).

At best, the US will slowly turn into Qing China. Unrivalled in its sphere of influence, stagnant and complacent. The US has always had a very strong anti-scientific undercurrent and a lot of it was kept in check by importing foreign elites wholesale (fairly sure the US public school system up to university level is nothing to write home about, on average). If the US turns against foreigners, most of the good ones will stop coming.

Now? No. But West Germany alone had 5000 main battle tanks in 1989. Demographics have changed, the economy has changed, but Europe could definitely project force all over the area about 1000-1500km in its vicinity if it really wanted to.

But Europeans definitely do not want that and up to a point, that's a good thing, yet Europe still needs a big enough force as a deterrent, and it currently does not have that.