I am not a lawyer. So this is worth squat. If the Fed law says:
(1) To prohibit causes of action against manufacturers, distributors, dealers, and importers of firearms or ammunition products, and their trade associations, for the harm solely caused by the criminal or unlawful misuse of firearm products or ammunition products by others when the
product functioned as designed and intended.
https://www.law.cornell.edu/uscode/text/15/7901
If the President by his action caused the bump stocked gun to classified be a 'machine gun' and the gun's designed easily allow that to happen, the protection of the clause
product functioned as designed and intended could be seen as void by a judge or jury. It was not the normal use of the gun and the design allowed it easily to be used in that fashion.
I can easily see a judge with a specific viewpoint and a jury sympathetic to the victims going for it. The implications though are risky. HCM posted about the import of Glock parts to make them fully auto. If someone went off with one of those modified guns - would a similar lawsuit be possible?
The Donald's actions enhanced the lawsuit's viability. Also, the secret plan of the NRA to throw the bump stocks under the bus to stop as they claim the unstoppable, extreme AWB from passing, might set a precedent to take down guns that simple parts can be made to be fully auto. Oops - if that occurs.