Well it is constitutional to prohibit persons under permanent domestic abuse restraining orders to surrender guns. But those orders require a full court hearing with counsel and typically a person has already been found guilty of some abuse.
The dividing line is whether a person could be ordered to surrender weapons before a full court hearing, so long as the hearing has to be held, and his guns returned if it's not shown he's dangerous. The NRA is opposed, no matter who gets killed, because once we pass that line, then it's a shorter hop to having to prove you're "competent" to own guns.