Trump can't cut off trade with Spain because it's part of the European Union. He would have to cut off trade with the whole EU, which would be a calamity for the US.
That's the idea of trading blocs like the EU, they give collective bargaining power for smaller countries so they can stand up to larger countries. Trade blocs do for small countries what unions do for workers.
The reason big countries try to split up trading blocs is because a united bloc can stand up to them. It's the same reason corporations try to split up unions.
On the other hand, Trump CAN cut off trade with the UK because it left the European Union.