The EU's tariffs are perfectly legitimate according to world trade law. If the US wants to push for advances in world trade law so that tariffs and non tariff barriers come down, then it would do well to start by ending its war on the WTO appellate body and world trade law more generally. What are the chances of that happening under Trump? You can't say you love tariffs and it is your favourite word and then say "sorry your tariffs are too high, what happened to free trade???"
This is hilarious. The US and Trump can continue down this path and force the EU to the table, and there’s precisely 0 anything anyone can do about it. No need to bother with any international bodies.