Despite all the hoopla about sweeping changes to the US-Mexico relationship, these things don't happen overnight. Among other things, the economic ties are so
Simply in terms of visas, there are a few roadblocks to 'stopping all the Mexicans':
- Most illegal immigrants don't cross the border covertly at all. They simply overstay their visas.
- Visa and immigration policy is set by Congress. Visa policy - at least as it relates to qualifying for a tourist visa - is essentially uniform around the world.
- Consular decisions are non-reviewable. They cannot be overturned by anyone. Of course, someone could always manually issue or deny a visa, but that's not a practical course of action for millions of visas.
