Comment by RHSeeger

Challenge.

Laws cannot an action a crime after it was committed. However,

- Civil rules can and do impact things retroactively

- Laws may not make something illegal retroactively, but the interpretation of a law can suddenly change; which works out the same thing.

- The thing you're doing could suddenly become illegal with on way for you to avoid doing it (such as people being here legally and suddenly the laws for what is legally changes). This isn't retroactive, but it might as well be.

It is _entirely_ possible for someone to act in a way that is acceptable today but is illegal, or incurs huge civil penalties, tomorrow.