The ATF's decision to treat bump stocks as machine guns is unconstitutional. Only Congress can make laws, and the administrative state is overreaching by suddenly defining devices that were legal from 2008 to 2017 as bannable. If gun-control advocates on the left want to push a ban on bump stock, they're free to do so through the legislative process — but gun rights advocates will then be able to challenge that on Second Amendment grounds.
It's unconscionable that those on the right side of the political aisle in the most violent industrialized nation on Earth are willing to allow these lethal devices to proliferate over a question of grammar. The ATF has the power to define what's a machine gun, and that means bump stocks are as bannable under this definition. If the conservative-majority SCOTUS doesn't rule that way, it'll be another sad chapter in the fight against excess gun deaths.