My Company (no, sorry; not my Company any more - it now belongs to a bigger Company) is holding an active shooter training in about 5 weeks. We've done this before, annually, and it attracts a full roster of federal, state and local LE personnel. It is held in a purpose-built facility with good guy and bad guy actors, simunitions, smoke bombs, moulage, sound effects, flashbang grenades - the works. Even hardened LE professionals come out of these drills with their knees shaking.
I just wrote to my former partner who was our CEO before the acquisition, and asked him to invite the Donald.
We could even offer free training to some of the USSS people we supply....
Let him go through THAT, and see if he still wants to give guns to teachers...
Simply putting him through some use of force training would help. I strongly suspect he would pull the trigger on all manner of innocents.