Another set of atrocities, this time in San Bernardino, Calif., has Americans wondering whether anything can be done to lower the body count. Many angry voices on the left have been saying that we could reduce the bloodshed if not for the National Rifle Association and its sympathizers. But they overestimate what gun control can achieve and underestimate the extent to which their own partisan emotion is an obstacle to progress.

Sen. Chris Murphy, D-Conn., illustrated the growing rancor of the debate. After the Newtown massacre in 2012, he tweeted his appreciation of the “thoughts, prayers, and words of support” from his colleagues in Congress.

Now he has had it with such sentiments. Thursday night he tweeted, “Your ‘thoughts’ should be about steps to take to stop this carnage. Your ‘prayers’ should be for forgiveness if you do nothing — again.”

You can see what he’s getting at. Saying that your “thoughts and prayers” are with the victims of a mass murder is a hollow gesture if you are refraining from taking obvious and practical steps that would make future massacres less likely. But have gun controllers, including Murphy, actually identified such steps?

It is not a self-evident truth that the main gun-control proposals that have been advanced in recent years, from a renewed ban on assault weapons to expanded background checks to restrictions on gun buying for people on the no-fly list, would have appreciably reduced murder rates; or prevented Newtown.

The assault-weapons ban in particular is a symbolic gesture: It prohibits some guns and allows others that are just as dangerous. The Justice Department’s most recent review found no evidence that the ban had any effect on crime rates. And of course Murphy was commenting too early to know whether any of these proposals were relevant to Wednesday’s shootings in San Bernardino.

Much of the debate over gun regulation founders on this basic truth: The proposals that have mainstream support are unlikely to achieve dramatic results, and more ambitious proposals are both practically and politically hopeless.

It’s a point that proponents of tighter regulation often evade. While the killers in San Bernardino were still being hunted down, Slate urged Americans to re-evaluate “what liberty truly means.” The right to own guns is a “newly invented” liberty, wrote Mark Joseph Stern: The Supreme Court only embraced it in 2008. He continued: “Mothers, daughters, brothers, fathers, sisters, husbands, and wives are being slaughtered every day by guns. Their blood is being shed in the name of liberty.”

It’s a preposterous remark, but only because it takes a typical mistake of the gun debate too far: treating constitutional principle and moral indignation as though they settled everything important. Maybe the Supreme Court’s decision was flawed as a matter of constitutional law, but the evidence that it has made our streets less safe is non-existent. Murder rates have kept dropping since it came out.

Probably it’s true that we would have a lower murder rate if we had fewer guns, as the regulators always say. But what follows from that proposition? Americans have hundreds of millions of guns. We are not going to get rid of them. That’s not because the National Rifle Association or the gunmakers’ lobby or a contested conception of liberty stand in the way. It’s because of the overwhelming opinion of the public — 72 percent oppose a ban on guns — and the practical impossibility of confiscation.

I’m not a gun nut: I believe there is a right to own guns, but it’s not absolute. Nor am I counseling fatalism. My colleagues at National Review have suggested three reforms: “We might move to prosecute anybody who has reasonable cause to believe that he is availing a dangerous person of a firearm. We might insist that to have knowledge that a person represents a grave and imminent threat to others is to have a legal responsibility to inform the authorities. We might look to reform our lax treatment and commitment laws, which leave too many at-risk individuals on the street, suffering from hallucinations and delusions over which, without medication, they may have little control.”

These ideas seem to me to be a more promising anti-violence agenda. But if politicians and activists take them up, they should not exaggerate the difference they would make or treat skeptics as the enemies of decency. And they should not disguise the modesty of the good their proposals would achieve behind the drama of a grand battle against the wicked.

Sen. Murphy is right that we should be thinking about what we can do to prevent mass shootings. But the existing agenda he and his allies are pushing is a distraction from that goal, and their posturing against their political enemies undermines it.

Like too many in the gun debate he is engaged in an empty ritual, an incantation, a prayer that we know will not be answered.

Ramesh Ponnuru is a Bloomberg View columnist.