No, it wasn't a brilliant move, it was just optics.
Federal law provides for declaring certain organizations "foreign terrorist organizations," a declaration which has legal consequences. But there is no such thing under federal law as a "domestic terrorist organization." President Trump could have officially declared antifa "a big bunch of poopy heads," and it would have the same legal significance.
Individual members of antifa can of course be punished for their crimes, and anyone who aids and abets a crime can likewise be punished. But antifa as an entity cannot be punished under current law, nor can anyone be punished for supporting antifa without tying them to a specific crime committed by a specific individual.
Bttt!
ANTIFA is not a domestic organization. Its international! Ask Great Britain and France about them.