I think you may be underestimating Europe. National militaries is one thing, and pop culture understanding of the region is another, but you'll find plenty of armaments and munitions in private care all across Europe. Not to mention how some Baltic and Slavic countries are still armed to the teeth, despite having a deficit in military spending.

In any case, the complaint about Europe not spending enough on military is a tired argument, because Europe wasn't neglecting their military - Europe was literally told to remove large swathes of industrial military complexes.

For more info, ask an African, the Chinese, the global south, everyone told Europe to put their guns down - and all across Europe military assets ended up in private hands.

The joke being that in the cities you won't find much guns, but travel out to the country and you'll find large showrooms.

But yeah, if the US betrays Europe, that might be the final nail in the coffin for European and US relations, so much so that I think the CIA would just drop Trump to avoid diplomatic suicide.