On a lot of issues these days, even Americans with considerable faith in government seem capable of recognizing limits to what public policy can achieve.

It’s widely argued, for example — especially among progressives — that America would be hard-pressed ever to achieve genuine “control” of its 2,000-mile border with Mexico — to truly seal off illegal immigration with a physical barrier, or an army of frontier guards, or both.

And such an effort, it’s said, would require a level of domestic militarization obnoxious to American values.

Similarly, it’s widely declared — surely not least by progressives — that any Donald Trump-style plan actually to deport 11 million illegal immigrants is a fantasy.

Any serious attempt at mass deportation would take years, maybe decades, we hear — and would involve oppressive police-state tactics even more alien to American ideals of liberty, privacy and limited government.

Realism likewise dominates discussion of the war on drugs, which is widely decried as a failure (again, especially by progressives). We haven’t succeeded in shutting off the drug trade or preventing drug abuse, we’re told. We’ve only succeeded in filling our streets with rivers of gang-fued bloodshed — while overcrowding our prisons with small-time drug offenders.

And the drug-war disaster, of course, is seen simply as an echo of the lesson we should have learned from Prohibition — the great historical example that proves the utter futility of trying to enforce laws that conflict with deeply rooted cultural practices.

There’s considerable truth in these dry-eyed assessments of the immigration and drug-war enforcement realities.

Somehow, though, such sobriety about government’s limits dissipates in many quarters when the discussion turns to gun control — usually, and heartbreakingly, in the wake of a nightmare like the recent college shooting in Oregon. Suddenly, it seems government’s capacities are not to be seriously questioned. It’s assumed we could control guns better than we control the border, and could convince Americans to “just say no” to guns, if not to drugs.

In his indignant speech to the nation the day the news from Oregon broke, President Obama gave an example of this confidence, essentially declaring that government could readily solve America’s unique gun violence problem if only politics didn’t stand in the way.

Obama dismissed “the notion that gun laws don’t work, or just will make it harder for law-abiding citizens [while] criminals will still get their guns …” He cited other nations whose laws have been able to “almost eliminate mass shootings.” And he concluded “So we know there are ways to prevent it.”

The president also made clear what he believes the objective of America’s gun policy needs to be: “It cannot be this easy,” he said, “for somebody who wants to inflict harm on other people to get his or her hands on a gun.”

It’s useful to keep that serious, concrete goal in mind, because of course at one point Obama fell back on the soothing reassurance that he only sought “common-sense” gun laws, which brings to mind expanded background checks and gun licensing and limits on magazines and so on.

Now, like most Americans, I have no objection to most such “common-sense” gun regulations ­— and it does seem preposterous that the gun rights lobby resists them all so inflexibly.

Except for this: Gun rights defenders are correct that none of these inoffensive regulatory measures would do anything meaningful to meet Obama’s stated goal — making obtaining a gun seriously difficult for “somebody who wants to inflict harm on other people.” And to be frank, we mean — in the case of mass shootings — somebodies obsessed and possessed, night and day, with the idea of harming people. In the case of ordinary gun crime, we mean cool and practiced lawbreakers.

No, keeping guns out of the hands of such people as these could be achieved only by genuinely strict gun laws — along the lines of the severe gun laws in force in those “other nations” Obama envies. Or, for that matter, laws along the lines of those that actually were in force in Washington, D.C., and Chicago until the U.S. Supreme Court struck them down as unconstitutional a couple years back — much to the outrage of progressives. Those laws were for practical purposes bans on private ownership of anything other than hunting guns.

Now, for the moment, let’s set aside the political (and legal) obstacles such a project might face. My purpose here is simply to return to the question of the limits of government’s enforcement powers ­— to invite readers to think about how successfully government really could enforce what would amount to a kind of gun prohibition.

It’s not impossible to imagine problems. Just as it might be toilsome to round up 11 million illegal immigrants, just rounding up guns already in circulation in America might be a bit of a chore. Obama noted that “there is a gun for roughly every man, woman, and child in America.”

OK, 320 million guns, give or take. Let’s get started. Confiscate (or buy back) 100,000 guns a day, every day, all year long, and after four long years — you still wouldn’t have half of them off the streets.

What staffing would that program require? What kind of enforcement tactics might be needed?

Is there any chance that a profitable black market in illegal guns — rather like the drug trade — might develop in response to firearm prohibition? Is violence imaginable as rivalries arise for control of the lucrative illegal gun trade? Might there be corruption, or a deterioration in respect for the law? Might a few small-time gun dealers or nonviolent gun owners land in prison?

Well, it’s worth some thought, even though we’re not likely to test the practicality of gun prohibition anytime soon.

And this thought experiment isn’t just for frustrated supporters of gun control. Those readers who can most vividly picture all of the impossibilities in a gun crackdown might want to ask themselves whether their thinking about, say, immigration enforcement has been equally skeptical and tough-minded.

All of our debates might improve through a commitment to a bit more consistency and care in thinking ideas through.


D.J. Tice is at Doug.Tice@startribune.com.