re: Trump Trial: Judge Merchan won't allow certain Defense testimony

Expert testimony about the law is typically not allowed. The judge is supposed to explain the law to the jury in the jury charges.

The parties can shape those jury charges when they file their versions and in the charge conference.

Battling experts is a tradition of litigation. Expert battle about industry standards, whether a party's act violated standards, etc. However, experts generally do not battle about the law. Judges will sometimes allow experts explain law from a different jurisdiction. but the judge is the expert on the law. The judge typically should not permit expert testimony on the law.