Changing a law to charge someone after the fact and bring him to trial is called an “Ex Post Facto” law which is unconstitutional.
There are two clauses in the U.S. Constitution which prohibit this outrage.
Where legislation, “if applied to past conduct, would impact substantive rights and have retroactive effect, the presumption against retroactivity is triggered” (id. at 370). When the presumption is triggered, “a statute is presumed to apply only prospectively” (id.). “This ‘deeply rooted’ presumption against retroactivity is based on ‘[e]lementary considerations of fairness [that] dictate that individuals should have an opportunity to know what the law is and to conform their conduct accordingly’ ” (id.). “[C]areful consideration of retroactive statutes is warranted because ‘[t]he [l]egislature’s unmatched powers allow it to sweep away settled expectations suddenly and without individualized consideration’ and ‘[i]ts responsivity to political pressures poses a risk that it may be tempted to use retroactive legislation as a means of retribution against unpopular groups or individuals’ ” (id.).
“Changing a law to charge someone after the fact and bring him to trial is called an “Ex Post Facto” law which is unconstitutional.”
The problem is that this is not a criminal statute, which is to what the prohibition against ex post facto laws applies, just like the prohibition against double jeopardy only applies to criminal trials. You can’t be tried for the same crime twice, but you can be sued more than once over the same incident. I’m not saying it is fair, but it is reality.