Actually, what would be subject to dismissal is Tennessee's defense. It's a Federal court issue concerning a pre-standing Federal law. So no matter what formi it takes, Tennessee (or a Tennessee litigant) would be arguing against that law, which means the Feds would take the position of applying the law in the first place, and see any response from Tennessee as a defense against violating it.
The defendant would be free to argue that the Federal law was not Constitutional, on its face, and then cite, as evidence, the opinion of the Tennessee Legislature, through the enacted State Legislation.
It would be the Federal law, that would be tested in Federal Court, and the State Law would be used as evidence against the Constitutional legality of the Federal law.