GUN SHOW UNDERCOVER…. When it comes to purchasing firearms, there’s a pretty significant loophole — criminals who wouldn’t otherwise be able to buy a gun can go to a gun show and avoid a background check. Licensed firearm dealers have to run the check; private, unlicensed sellers at a show don’t.

It leads to a rather obvious phenomenon — criminals who can’t pass background checks go to gun shows and buy firearms anyway.

NYC Mayor Michael Bloomberg, a fierce critic of the gun-show loophole, launched an interesting investigation. Bloomberg’s office sent undercover investigators to seven gun shows in Ohio, Tennessee, and Nevada, to see how easy it is to exploit the gap in the law. The investigators secretly recorded their experiences.

Now, the existing loophole is supposed to have a safeguard — if a private seller has reason to believe a buyer wouldn’t pass a background check, it’s a crime to go through with the sale. So, as part of this investigation, the undercover officials specifically told gun-show sellers that they’d fail a background check.

And in 35 out of 47 cases, the sellers sold the guns anyway.

“The gun show loophole is a deadly serious problem — and this undercover operation exposes just how pervasive and serious it is,” Bloomberg said. “We are sending a copy of our detailed report Gun Show Undercover to every member of the United States Congress. We’ll work with congressional leaders to pass legislation closing the gun show loophole. This is an issue that has nothing to do with the Second Amendment; it’s about keeping guns from criminals, plain and simple.”

Of course, watching the undercover footage, it’s hard not to think about a certain other video we’ve seen recently with secret filming. As Karl Frisch sarcastically noted, “Since Fox News and Andrew Breitbart has been positively obsessed with the ACORN videos, I’m sure this will be right up their alley.”

We know it won’t, but the point is nevertheless important. The anti-ACORN videos sparked immediate congressional outrage and generated an enormous amount of media attention. It dealt with a couple pretending to be a prostitute and a pimp getting tax advice. The Bloomberg video is about criminals buying firearms. Which is more important?

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.