If they are charged then they'll be charged with state crimes. Trump has no authority to intervene in those.
The feds intervene in state and local crimes all the time.
Take for instances all the police officers charged federally on a regular basis because the feds feel the state is not prosecuting them enough for civil rights violations.
A prosecutor is no different and subject to the same federal jurisdiction.
The second amendment is a constitutional right and the local prosecutor has no authority to ignore it. He is breaking the law.
The left has been hammering us for decades using civil rights as a method to attack the right. It time we give them a taste of their own BS.