That has nothing to do with the current topic. Those are red flag laws and under the purview of the states, not the federal government.
When a family member was arrested, I had to swear to a federal judge that I would confiscate his weapons and prevent his accessing them until the case was adjudicated. That is exactly what happens under most state "red flag" laws. If the judge determines you should not have access to weapons, they can do just that. To get them back, you must prove that you are capable of responsible gun ownership. That is what Trump was referring to.