The U.S. Justice Department has acted — finally! — on a measure that well could start us down a more rational, sane world regarding firearm regulation.

DOJ announced it is going to implement a ban on bump stocks, those devices that turn semi-automatic firearms into fully automatic killing machines.

While the nation has been fixated since Valentine’s Day on the Parkland, Fla., high school massacre, let us remember an earlier slaughter.

A lunatic opened fire in Las Vegas with a semi-auto rifle he had converted into a machine gun, killing 59 people attending a music festival at Mandalay Bay Hotel and Casino. He eventually killed himself.

The debate over bump stocks was joined immediately.

Is this measure going to strip legitimate firearm owners of their right to “keep and bear arms”? Not in the least. It is going to potentially deter future madmen from doing what the Las Vegas shooter did, which is turn a semi-automatic rifle into a virtual weapon of war.

In announcing the Justice Department directive, though, we had to leave it to Donald Trump to lay blame on his made-up nemesis, Barack Obama, for “approving” bump stocks.

Trump’s tweet is sort of correct, at a certain level. The decision to allow bump stocks was done at an administrative mid-level at the Bureau of Alcohol, Tobacco and Firearms. The president or the attorney general, Eric Holder, had no direct input on the deliberations being undertaken.

Leave it to Obama’s successor, though, to forgo a forward-looking statement and to assess blame on someone else on a problem that needed to be fixed.

So, the Justice Department has acted. It will ban bump stocks. It will seek to prevent gun owners from creating machine guns.

This is by no stretch of anyone’s imagination a decision that launches us down any sort of slippery slope. It makes sense.