Vice President Joe Biden, after a week of meetings with almost every imaginable stakeholder in the Great American Gun Debate, is no doubt crafting the list of gun policy recommendations he is expected to deliver to President Obama on Tuesday. Among them, by most accounts, will be a proposal for “universal background checks” on prospective gun buyers.

The vice president himself was almost effusive regarding that notion, saying early Thursday that “there is a surprising, so far, recurrence of suggestions that we have universal background checks.”

But wait, you say, aren’t gun buyers already required to undergo criminal background checks? And what, skeptics ask, do such checks have to do with preventing massacres like the one last month at Sandy Hook Elementary School, in which the shooter himself never even bought a gun?

Here’s a background-check primer to help you understand the current law of the land, how it might change, and what a reform would – and wouldn’t – accomplish.

Why have background checks?

The idea is to keep firearms out of the hands of known criminals, fugitives, drug addicts, the mentally ill, and domestic violence perpetrators. To that end, Congress established the National Instant Criminal Background Check System (NICS), which became operational in late 1998, to check the names of prospective gun buyers against databases that track the above classifications. The system is managed by the FBI.

Where and when are checks required?

Those in the gun business – manufacturers, importers, dealers – must obtain a federal license, and all licensees are already required to run a background check before selling a firearm to a buyer. This is true whether the licensee is selling firearms from a store or at one of the thousands of gun shows held each year across the United States.

However, after an individual has bought a gun, he or she is free to sell it to another – a relative, a friend, or a stranger – without obtaining a background check on that new buyer. These so-called “private sales” sometimes occur at gun shows, leading reformers to decry the “gun show loophole.” These private sales are the target of any move to require “universal” background checks.

How often do background checks prevent a gun sale?

More than 100 million background checks have been run in the 14 years the NICS has been in place. As of the close of 2012, sales have been denied 987,578 times, the FBI reports.

The top reason for a federal denial – 577,814 instances – is that the prospective gun buyer had been convicted of a crime punishable by more than one year (or a misdemeanor punishable by more than two years). In 143,852 cases the basis for denial pertained to domestic violence – either a restraining order or a misdemeanor conviction. Mental health, believed to be pertinent in the Virginia Tech massacre, the Colorado movie theater shooting, and the slaughter of innocents in Newtown, Conn., was the reason for an NICS denial in 10,180 cases.

Of course, it’s impossible to know whether denied individuals were subsequently able to obtain firearms through a private sale or theft.

What share of gun sales is private, without background checks?

A number is hard to come by. The Brady Campaign to Prevent Gun Violence, which has spearheaded the drive for tougher gun laws, says at least 40 percent of firearms are acquired without background checks, citing a 1996 study done for the Police Foundation.

Who favors universal background checks, and why?

Gun control activists say it’s ludicrous to exempt some gun buyers from criminal background checks, and that public safety and common sense demand redress, preferably by a federal law. Absent federal action, they are pushing states to require unlicensed gun sellers at gun shows to run background checks on prospective buyers.

Private sales, especially at gun shows, are a chief way that criminals and other dangerous individuals get their hands on firearms, they argue. Criminals themselves may not necessarily buy at gun shows, but the folks they buy firearms from do, the argument goes. Being able to track a gun’s ownership is vital to identifying the traffickers who sell to criminals.

Besides the Brady Campaign and other gun-control advocacy groups, groups backing the idea of broadening background checks include the International Association of Chiefs of Police and the 700-strong Mayors Against Illegal Guns.

There are some signs that broadened background checks may be able to win political support from some moderate Second Amendment supporters. Richard Feldman, president of the Independent Firearm Owners Association and one of those who met with Mr. Biden, wrote Thursday on the group’s website in a plea for public civility, “Let’s agree to require the National Instant Criminal Background Check System (NICS) at gun shows.”

And Robert VerBruggen, writing on the The Corner blog for the conservative National Review Online, had this to say: “Universal background checks would help us hold people accountable for giving guns to criminals. When the police traced a gun to the original buyer, that person could no longer simply say he didn’t have it anymore; unless he’d documented a sale and conducted a check (or filed a police report claiming it was stolen), he could be investigated for an illegal transaction. This would make straw purchases more risky and prevent criminals from buying guns freely from private citizens.” Universal background checks, he concluded, “is certainly not the worst idea the gun-control crowd has come up with.”

Who opposes universal checks, and why?

The National Rifle Association is leading the charge against expanding criminal background checks to private gun sales. Its key objection is that such a step would be ineffective – it would not keep guns out of the hands of criminals and not do anything to protect children in schools. It would just create another layer of regulatory red tape with which law-abiding citizens would be forced to contend.

Moreover, opponents say universal checks are irrelevant to the problem at hand: keeping schools safe. “It feels like [the discussion] is turning into a ramped-up version of the same old gun-control arguments,” said Cam Edwards, host of “Cam & Company” on NRANews.com, on his show Thursday. “Meanwhile, we still have the issue of our kids and safety in schools, and that’s being shoved aside….”

Many gun-rights advocates argue, too, that Congress is unlikely to adopt proposals that smack of new restrictions on gun owners. Whether a universal background check falls into the "bridge too far" category may depend on the specific details of its cost and how it would be carried out.

And lest anyone worry that the National Review has lost its conservative bearings, here’s the magazine's Jim Garaghty during an appearance Thursday on “Cam & Company”: “The legislative solutions that are proposed [after a tragedy such as the Newton, Conn., school shootings] very rarely have anything to do with what happened…. After the Virginia Tech shooting, the preeminent discussion from Mayors Against Illegal Guns and [New York Mayor Michael] Bloomberg and all these groups was, ‘We have to close the gun show loophole,’ even though the shooter at Virginia Tech didn’t get his guns at a gun show.”

Have universal background checks been tried anywhere?

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Seventeen states have taken some kind of step to beef up background checks at gun shows, according to the Brady Campaign. Among those are California and Rhode Island, which require such precautions for all sales of guns, including private sales. California does this by mandating that all gun sales go through licensed dealers for background checks, and that service can cost a private seller $35 per buyer.

“California's regulatory policies were associated with a decreased incidence of anonymous, undocumented gun sales and illegal straw purchases at gun shows. California gun shows were not hurt by the restrictions,” concludes the Brady Campaign on its website, citing a 2007 study published in the journal Injury Prevention.