Almost every Democrat running for president supports so-called “gun buybacks.” Too bad they don't work.

Proposals range from Joe Biden's voluntary gun buybacks to the more radical mandatory confiscation proposed by Cory Booker. (He still misleadingly calls it a “buyback.”) So it’s worth examining how such buybacks played out recently in New Zealand, which passed a ban on the sale of semiautomatic weapons and a mandatory gun buyback program after a tragic shooting in April.

The deadline for the mandatory gun buyback program was Friday. The New Zealand program successfully led to the compensated confiscation of 51,000 of the targeted firearms . But as the left-leaning Guardian newspaper reports , this is out of an estimated 170,000 such guns currently in circulation. And there are still a minimum of 1.2 million legally owned firearms in New Zealand on top of that.

This means that many people ignored the demand that they turn in their guns and trust the supposedly benevolent government to protect them from themselves.

And it’s almost certainly safe to say that those who surrendered the 51,000 semiautomatic guns will skew heavily toward the law-abiding, nondangerous end of the spectrum. Thus, getting these guns off the street in this fashion only tends to disarm the good guys, leaving their society at large more at risk, not less. Americans use firearms in self-defense hundreds of thousands of times per year, analysts estimate , usually without firing a shot.

One must avoid drawing direct conclusions based on how policies affect countries with different populations, characteristics, and societal norms. But rough comparisons can be fair, for what they're worth. And the massive failure of what was a sweeping, bipartisan gun control measure in New Zealand bodes poorly for how more obstreperous Americans would react to the partisan, contentious gun control measures Democrats are contemplating.

Moreover, assuming that American gun owners complied in similar proportions, common sense dictates that those planning to use their guns to commit crimes would be among the last to comply. Meanwhile, millions of people in the United States who pose no threat would become criminals overnight. They could face incarceration or even deadly consequences if police really do go around kicking in doors to seize guns, as failed presidential candidate Beto O’Rourke once called for.

And even in the case of a voluntary buyback, it is far less likely to attract guns that are going to be used in crimes.

All in all, New Zealand’s mandatory buyback program is a massive failure. But don’t expect that to change the minds of most Democratic presidential candidates. They’re concerned with what polls well among the Democratic base — not with what actually works.