Of course they can, but not before the jury. Under those federal rules, the judge determines what the law is, including if it's a law at all, while the jury determines the facts of the case. That is, did the defendant violate the "law", not "what is the law, is it valid or not?".
" Of course they can, but not before the jury.
The issues involved would have the effect of putting the law directly on trial. That can't be done in a trial court. The trial court must take the law and precident at face value.