The left is dumbfounded. Normally the folks just act like good sheep and comply. What will they do now?
They will confiscate unregistered firearms found incidentally during a low-risk police activity (like enforcing a summons for a parking ticket), and then make a high-profile prosecution on that charge.
The search which discovers the firearm(s) will be warrantless, unlawful, and invalid. Charges may be dismissed or nullified by a Jury. The law itself may be successfully appealed and ruled to be unconstitutional. It won't matter. "The process is the punishment".
Repeat as opportunity presents itself.
This will backfire when the firearms owner turns out to be a registered Democrat - and one of the state legislators.