In 2018, following a deadly 2017 mass shooting in Las Vegas, and at the urging of then-President Donald Trump, the Bureau of Alcohol, Tobacco, Firearms, and Explosives classified "bump stock" attachments for semiautomatic rifles like the AR-15 to be "machineguns" that are strictly regulated under federal law.

On Friday, a 6-3 majority of the Supreme Court ruled that the 5th Circuit Court of Appeals was correct in determining that the ATF "exceeded its statutory authority" in banning the civilian possession and use of bump stocks, according to The Hill.

The decision, which was centered on bureaucratic overreach and did not specifically implicate Second Amendment-protected gun rights, nonetheless elicited a furious response from anti-gun Democrats and gun control groups.

ATF reclassified bump stocks as "machine guns"

At the heart of the case known as Garland v. Cargill is a statute that stems from the National Firearms Act of 1934, 26 U.S.C. § 5845(b), which was promulgated in response to the increasing criminal usage of automatic weapons and "machineguns" and largely banned such firearms from civilian possession and usage with strict regulations.

The statute defines a "machinegun" as "any weapon which shoots, is designed to shoot, or can be readily restored to shoot, automatically more than one shot, without manual reloading, by a single function of the trigger," and also includes certain parts that would convert an ordinary weapon to fire multiple shots with a "single function of the trigger."

The ATF, after years of saying otherwise, arbitrarily reclassified bump stocks as "machineguns" because the attachment simulates automatic fire by using the weapon's recoil, plus constant forward pressure from the shooter, to rapidly engage, reset, and reengage the trigger to fire multiple shots in quick succession.

The statutory definition is key

In the majority opinion authored by Justice Clarence Thomas, the "single function of the trigger" aspect of the statutory text is key and is what differentiates a semiautomatic rifle, even if equipped with a bump stock, from a traditional fully automatic machinegun.

"Semiautomatic firearms, which require shooters to reengage the trigger for every shot, are not machineguns. This case asks whether a bump stock -- an accessory for a semiautomatic rifle that allows the shooter to rapidly reengage the trigger (and therefore achieve a high rate of fire) -- converts the rifle into a 'machinegun.' We hold that it does not and therefore affirm" the circuit court's ruling," the majority concluded.

The reason for that, as Thomas explained at length and with the aid of multiple diagrams and graphics, is that while the trigger only needs to be pulled once on an automatic weapon for continuous fire, that same trigger must be repeatedly moved and reset to fire a single shot with a semiautomatic weapon, even with the aid of a bump stock.

"With or without a bump stock, a shooter must release and reset the trigger between every shot. And, any subsequent shot fired after the trigger has been released and reset is the result of a separate and distinct 'function of the trigger,'" Thomas wrote at one point. "All that a bump stock does is accelerate the rate of fire by causing these distinct 'function[s]' of the trigger to occur in rapid succession."

Justice Samuel Alito authored a brief concurring opinion that seemed to support the idea that bump stocks are particularly lethal and should be banned but pointed out that only Congress, and not the ATF by itself, had the authority to do so.

He wrote, "There is a simple remedy for the disparate treatment of bump stocks and machineguns. Congress can amend the law -- and perhaps would have done so already if ATF had stuck with its earlier interpretation. Now that the situation is clear, Congress can act."

Sotomayor's dissent and anti-gun outrage

According to CNN, Justice Sonia Sotomayor wrote a dissenting opinion, which she read aloud from the bench, that sharply disagreed with Thomas' focus on the internal mechanics of how a trigger works and even resorted to the "if it looks like a duck" analogy to insist that bump stock-equipped semiautomatic rifles were no different than fully automatic machineguns and should be banned.

The outlet also noted the immediate outcry from anti-gun Democrats, including President Joe Biden, and gun control groups who decried the court majority's "deadly" and "shameful" decision to overturn the ATF's ban on bump stocks.

As for the man behind the case, a Texas gun store owner named Michael Cargill, The Hill reported that he said of the court's ruling, "Over five years ago I swore I would defend the Constitution of the United States, even if I was the only plaintiff in the case. I did just that."