Dylann Roof shouldn’t have been able to buy a gun. That likely won’t change the gun debate.

Mourners place flowers outside the historic Emanuel African Methodist Church in Charleston, S.C., where nine people were shot to death. (Chip Somodevilla/Getty Images)

[This post has been updated with the latest information about Roof's criminal record when he bought a gun.]

When Dylann Roof tried to buy a gun, he shouldn't have been able to do so. And it was a record-keeping error in the background-check process that allowed the accused Charleston shooter to do it.

The fact Roof had admitted to possessing drugs somehow slipped through the FBI's screening system, which should prevent such people from buying a gun, the FBI said Friday.

[Dylann Roof had apparently not been arrested for a felony]

"This case rips all of our hearts out, but the thought that an error on our part is connected to a gun this person used to slaughter these people is very painful to us,” FBI Director James Comey said.

It's a striking and very sad admission. And it's also easy to see how that error could quickly become a sizable piece of the still-simmering gun debate.

But it's also unlikely to change much of anything, because both sides are likely to see this as vindication of their position.

Supporters of tighter background checks can argue this proves the system needs to be revamped and improved. It didn't work, after all.

"One immediate response," Democratic presidential candidate Hillary Rodham Clinton said the day after nine black church members were shot and killed in Charleston, "was to ask how it could be possible that we as a nation still allow guns to fall into the hands of people whose hearts are filled with hate?"

[Hillary Clinton's push on gun control marks a shift in presidential politics]

But gun-rights supporters will surely argue we already have a common-sense system in place -- and that the system in place should indeed have stopped Roof from getting a gun. The fact that it didn't do that suggests a failure of individuals, not the system, they will argue.

The reality is that even though about 90 percent of Americans consistently support universal background checks, gun laws aren't likely to change anytime soon in our country.

[The sad reality of how we feel about mass shootings, in 3 charts]

Part of that is because a majority of Americans also don't generally think we need new gun laws (even though the current system isn't quite universal), and another part of it is that Americans largely don't think we can do much to prevent mass shootings like the one in Charleston.

It's also because the gun-rights lobby has a decades-long head start on gun-control groups in fundraising, organizing and mobilizing its members to take political action. A 2013 Pew Research survey found 25 percent of gun-rights defenders have given money to an activist organization on the issue, while just 6 percent of gun-control supporters have.

But even if the debate were evenly matched, we doubt this latest, tragic news would do anything to change it. The two sides are ensconced, and Friday's news will provide some form of self-confirmation for both of them.