Quite sensibly, the A.T.F. realized it needed to take another look at the issue of whether certain armor-piercing bullets that had long been associated with rifles were now more problematic because they could be used in these new, more lethal handguns. Agency employees met with industry representatives and law enforcement officials. And last month, the A.T.F. published a document outlining a new framework for deciding whether certain bullets that had been exempt should now be banned. One bullet in particular, widely used by AR-15 owners and described by the A.T.F. as “5.56-mm projectiles in SS109 and M855 cartridges,” would be banned under the new framework. Why? Because if used in handguns, they could kill cops.

Which, of course, leads to the second thing that has changed. Congress no longer passes bills opposed by the N.R.A., even if the intent is to save the lives of police officers. Indeed, in the Obama era, the right-wing echo chamber is quick to label even an effort as benign — and as sane — as the A.T.F.’s proposed framework as yet another example of the president abusing his authority.

The N.R.A. quickly labeled Obama a “dictator.” Pro-gun bloggers screamed about this latest assault on their Second Amendment rights. “[Obama] wants to take guns out of everybody’s hands, and if he can’t do that, he’s gonna take the bullets,” said Mr. Echo Chamber himself, Rush Limbaugh.

And Congress? This week, 239 House members — more than half of the House of Representatives — sent a letter to B. Todd Jones, the director of the A.T.F., telling him, in effect, to buzz off. (“The effects of these restrictive interpretations are untenable.”) Jones will soon be getting a similar letter from the Senate side. It is hard to imagine that the A.T.F., already under siege, thanks to its botched Operation Fast and Furious, will be able to withstand this much congressional pressure.

On Friday morning, I spoke to one of the more thoughtful House conservatives, Scott Rigell of Virginia, who had signed on to the letter. I told him I couldn’t understand why there was such a furor over armor-piercing bullets that could kill police officers. “When I first heard about this,” he said, “I was truly stunned.” He had three objections. First, the ammunition in question is widely available and has never been a problem for the police. Second, he agreed with those who said that the administration was trying to impose its “deeply held views” on the country by fiat. And third, he felt that this could be the proverbial slippery slope. “If you conclude that this round is armor-piercing, then you have opened the dam completely,” he said.