The EU unsuccessfully tried to save the JCPA (aka "Iran nuclear deal") from US sanctions by creating an alternative financial payment infrastructure based on the Euro & European banks & side-stepping sanctions as enforced by the US Treasury.

It totally would have worked, had the US not escalated to sanctioning any entities that dared to utilize this alternative system to deal with Iran. You are right to say the EU needs to get a bigger stick to successfully protect its interests when they diverge from American interests. In the long term - I'm talking decades - American troops will leave Europe, perhaps leaving a skeleton crew managing nuclear deterrence: whether they will be pulled back, or pushed out remains to be seen, but the natural evolution of the EU project will eventually result in a standing European army. What happens on Nov 3 will accelerate or delay this eventuality