A chilling Internet video confirms what has long been suspected: Al Qaeda terrorists are eager to launch a gun-fueled rampage against Americans - and they know just how to do it.

Spotted on jihadist forums, the video shows American-born Al Qaeda fighter Adam Gadahn almost cheerily urging followers to action:

"America is absolutely awash with easily obtainable firearms. You can go down to a gun show at the local convention center and come away with a fully automatic assault rifle without a background check and most likely without having to show an identification card. So what are you waiting for?"

We don't say this often about Al Qaeda types, but: He's right on the facts.

Gadahn owes thanks to the National Rifle Association, whose political muscle has kept open two indefensible gun-rights loopholes that all but invite terrorists to buy weapons.

Unlike those who purchase guns from a dealer, people who buy firearms from private sellers at gun shows don't have to pass a background check.

The Bureau of Alcohol, Tobacco and Firearms says 30% of illegally trafficked weapons are linked to gun shows. In fact, an undercover investigation of private sellers at gun shows found that nearly two-thirds broke the law by selling to people who they thought could not pass a background check.

Then there's the so-called terror gap, which prevents gun sellers from checking purchasers against terrorism watch lists. More than 1,450 people on terror watch lists tried to buy guns and explosives from February 2004 to December 2010; on 1,321 occasions, 91% of all tries, the FBI was powerless to stop the sale.

Common sense and national security argue powerfully for reform. The NRA and its allies argue reflexively against it.

In November 2008, radical Islamist terrorists killed 164 people and brought Mumbai to its knees with a coordinated rampage on targets including hotels, a cafe, a Jewish community center, a hospital and a movie theater.

To Al Qaeda, it was a moment of triumph. This is what Gadahn has in mind for the U.S. The NYPD is well aware of the threat.

Unless Congress develops the backbone to override the NRA on critical public safety measures, Mumbai could well be a preview of an American and New York horror.