If a Suppressor is a firearm as the DOJ is now declaring it is, Hawaii can't make it illegal to own or can they? 
Based on the cases I've read lately, the argument over what's a firearm is a catch 22 problem.
If you say a suppressor is a firearm so buyers have to jump through the same background check hoops as for firearms, then suppressors are by definition protected by the 2A and are not subject to outright banning if they aren't within certain exceptions, like WMDs.
On the other hand, if you call a suppressor an accessory and NOT a firearm, then there's no requirement for anyone to jump through the hoops to own one. Alone, a suppressor presents no danger to anyone.
This judge walks through the arguments as they relate to California's magazine restrictions/capacity limits. The government argues that a magazine is an accessory and therefore not afforded the same 2A protection as a firearm. Yet magazines designed for certain semi-auto firearms having > 10 rds are being controlled not as accessories, but as part of a firearm that allegedly makes them more lethal and dangerous. When the later argument is applied to other parts of a firearm, they backtrack to the rebuttal that the difference between what is a firearm vs. what is a firearm accessory is somehow well defined.
That second part has never been truly challenged in the Supreme Court. Before Bruen, the safety of the public at large was allowed to be considered in gun laws (balancing test). Post-Bruen, balancing tests are no longer allowed when determining the application of 2A protections.
This video ia a little long and somewhat complicated in some sections, butt the Judge does an excellent job of explaining things for the average person to grasp.