According to the National Rifle Association, background checks of gun buyers can never be universal because criminals will never submit to them.

Several recent cases in Maine, however, show how criminals who could not pass a background check can acquire guns easily because of the haphazard regulation that is as bad as no regulation at all.

According to federal law, felons are banned from owning firearms. So are people convicted of a misdemeanor charge of domestic violence assault. So are those who have been involuntarily committed to a hospital as a result of mental illness.

That’s why gun buyers have to go through an instant background check when they do business with a licensed firearm dealer. That requirement, however, is optional when they go to an unlicensed dealer.

It’s called the “gun show loophole” because that’s one place a person can sell a gun to a stranger without any background check. In Maine, it could be called the “Uncle Henry’s exemption” because the popular classified circular advertises scores of guns for sale by private sellers who don’t have to look into the buyers’ backgrounds.

An article by Kevin Miller (“Maine private gun marketplace thriving”), published on Sunday, outlines three cases in which a gun moved into criminals’ hands using the private sales loophole.

In one case, a Portland man with a felony history bought a handgun that was advertised in Uncle Henry’s. He sold the gun to a contact in New York. The gun was used in a shootout with New York City police.

A gun sold by its original owner at a gun show is known by Portland police to have been used in two homicides in the city, one unsolved. There was no background check and there is no record of the sale.

In yet another case, a Boston man was sentenced to 17 years in prison from running a weapons supply operation for his gang, using guns sold privately in Maine.

These cases expose the weakness of the NRA’s argument. It’s true that criminals won’t submit to a background check — they don’t have to. As long as there is a legal no-background-check market in at least one state, they can skirt the law and acquire firearms whenever they want them.

Cracking down on background checks does not infringe on the rights of legal gun owners, but it does make life more difficult for criminals. It may not make it impossible for a felon to get a gun, but closing the private-sale loophole would make guns harder to get. And there might be fewer guns available on the black market.

If gun owners can’t live with background checks in 100 percent of sales, maybe they would prefer being held liable for crimes committed using guns they sold without a check.

Under the current system, it’s too easy for guns to find their way into the wrong hands and for no one to take responsibility.