In the midst of all the buzzwords, Slate barely touches upon the central issue.
The NRA went into a state (PA) with a gun preemption law, and is forcing towns and municipalities to (gasp!) follow the law.
In my home, Washington state, this is accomplished by ordinary citizens who take it upon themselves to become freedom activists. OpenCarry.com has a lot of posts involving cities and counties getting called on illegal anti-gun postings in parks and public places. The cities always cave, because big-bucks Seattle got taken to the woodshed by WSC, in that the preemption law really means what it says.
florida did this with the addition that any municipal official who did not repeal such pre-empted laws was criminally liable.