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Mere hours after we woke up to the horrendous, terrifying news of the Aurora shooting, Mayor Michael Bloomberg took to the airwaves to criticize the candidates for their relative silence on gun policy. "Soothing words are nice," he said, "but maybe it’s time that the two people who want to be President of the United States stand up and tell us what they’re gonna do about it." Hizzoner, a longtime supporter of gun control initiatives, re-upped his comments on Morning Joe on Monday. We all know he’s got a point. But we also know that the prospects of congressional action on gun safety—and by extension the chances that the candidates will call on Congress to do something—are about zero, because the NRA has a chokehold on our elected legislators. How do they do it?

It’s pretty simple, actually: the NRA employs a rating system based on each member’s voting history. Here’s how it works. Before most votes having anything to do with gun rights, and even some that actually don’t, the NRA will announce that they will be "scoring" the vote, meaning that they will take this vote into account when assembling a letter grade to assign to each candidate. (Some sample grades are here.) In part because House members have to run for reelection every two years, the NRA grades have become a vital part of how candidates portray themselves to voters—and conservative and swing-district members will do everything they can to keep a good rating.

I asked a Democratic legislative staffer for a first-person description of the NRA’s power on the Hill. Here’s the response I got, on the condition that I not provide any further identifying information. It’s pretty breathtaking.