Actually the law itself might be Constitutional, but it would in effect never have been properly inacted, and thus not a law at all. Before they become laws, bills must be signed by the President, or passed over his veto by supermajorities of both houses of Congress. Any bill which he signed, would simply never have become law.
It would be one smell of a hess.
Yep, bad wording on my part. Should have said bill. Late at night ....