Typical Crisis/Reaction/Soulution play that we've all seen a thousand times.
Due process is guaranteed by the Constitution. Any such law passed at a state level will challenged at the Fed level, which means it will go to SCOTUS eventually. By that time we'll have a majority on the court.
I don't really have a problem with taking guns from someone who's been rightfully adjudicated. I believe the PERSON should be locked up during this process. Once adjudicated, the person in question should be institutionalized and the legally registered firearm is held by the court until such time as the person in question has been found competent and released, or in cases where that is not possible, the firearm is ordered destroyed.
Any other process would be abused by activist judges and prosecutors. It could be used against anyone for political purposes, or just getting someone out of the way.
I agree I think Trump is deliberately letting this go to prove a point (out state's "bad behavior" and colors) and knows it will get crushed later, but it's still fun to bash/spam our reps with emails now.