system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If states can defy federal law and legalize marijuana, then why can't they just start deporting illegal aliens?
gpt
The Supreme Court has said, multiple times over the past 200 years, that states have no authority whatsoever to regulate immigration.  The Federal government's authority over immigration is "plenary" (complete) and "unqualified" (there are no exceptions).

By contrast, states have always had authority to define crimes for themselves, and the the Federal government has a much more limited authority over crimes than the states.