Hillary Clinton has a new gun agenda that is the same as the old gun agenda.

We all are appalled and heart-sick over the country’s mass shootings, which aren’t any less shocking for their routine occurrence.

But that doesn’t mean we know how to stop them. The Pavlovian Democratic reaction is to offer a raft of familiar gun-control proposals, whether they have any bearing on mass shootings or not.

Hillary’s ideas are a testament to the essential sterility of the gun debate, no matter how much heat it generates. There is no way around the fact that marginal changes will do little or nothing to stop mass killers, while more sweeping changes — even if they were practicable or wise — run afoul of the Second Amendment.

Among other things, Clinton wants to renew the assault-weapons ban, which we had for 10 years before it lapsed in 2004. The ban never made any sense, and a push to revive it is nostalgia for a meaningless gesture. To review: A so-called assault-weapon is a semi-automatic rifle tricked out with frightening-looking cosmetic features. It is functionally indistinguishable from any other semi-automatic rifle.

Assault weapons might play an outsized role in crime in Hollywood productions, but not in real life.

Rifles generally aren’t used in shootings, let alone assault rifles. All rifles account for about 300 homicides a year. A Department of Justice-supported study of a possible renewal of the assault-weapons ban called its effect on violence “perhaps too small for reliable measurement.”

Clinton wants to close the “gun-show loophole,” which is one of the great cliches and myths of the gun-control debate. The loophole doesn’t actually exist. Federally licensed dealers have to run a background check or otherwise ascertain that a purchaser has passed one, even if the dealer is selling at a gun show. Private sellers don’t have to conduct one — whether or not they are selling at a gun show.

The inordinate focus on gun shows might make sense if there were evidence of an epidemic of criminals using them to get their weapons. There isn’t. A study in the journal Preventive Medicine of criminal offenders in Chicago found that most obtained their guns through personal connections. “Rarely,” the study said, “is the proximate source either direct purchase from a gun store, or theft.”

Clinton also seeks to tighten up background checks by not letting dealers automatically sell to a buyer if a check hasn’t been completed in three days. The problem with background checks as a means to stop mass shootings is that very often the shooters don’t have criminal records and haven’t otherwise been adjudicated. This makes it impossible to use background checks to stop them from buying guns.

If it matters, none of this has anything to do with the Oregon shooting. The killer apparently used handguns to mercilessly shoot down his victims (although he also had a rifle, an AR-15). All of his 13 guns came from federally licensed dealers. He passed background checks. What Hillary has done is take a national tragedy and declared that it ought to catalyze us to pass a series of non-sequiturs.

Not incidentally, the politics of her proposals are good in the Democratic primary. From gun-friendly (and low-crime) Vermont, Bernie Sanders opposed the Brady Bill in the early 1990s and is relatively reasonable on the issue. In the general election, though, Clinton is risking a fierce backlash. She promises to make her change in the “gun show loophole” through unilateral executive action, a pledge that couldn’t be better designed to activate the NRA.

Substantively, her proposals aren’t well-thought out, because Democrats don’t think when it comes to guns. They hold the same sub-rational belief that President Obama expressed in his impassioned post-Oregon statement last week: that preventing mass shootings is easily within our power, with enough political will. Would that it were so.