Just slapping a 10% tax on it would be great, the remittances have been running over $20 billion a year, so that would generate $2 billion a year for the US without killing the goose. Even 5% would still produce a gift that keeps on giving. Cutting it off entirely with a confiscatory tax would probably throw Mexico into chaos, it's something like a fifth of their GDP, and having the damn place' fail completely is really not in our own best interests.