At the beginning of last night's presidential debate, moderator Chuck Todd noted that even if Congress enacts a new federal ban on so-called assault weapons, which all of the Democratic presidential contenders seem to favor, "there will still be hundreds of millions of guns in this country." He asked the 10 candidates on the stage what, if anything, the federal government should do about that inconvenient fact. Their responses revealed that none of them has a satisfying, or even superficially plausible, answer to that question.

Sen. Elizabeth Warren (D-Mass.) said more research is needed.

Sen. Cory Booker (D-N.J.), who has proposed the most ambitious gun control program of anyone in the Democratic field, once again eschewed policy substance in favor of an emotional appeal, declaring that the issue is personal for him because "I hear gunshots in my neighborhood." What should be done about that? "It is time that we have bold actions and a bold agenda," he said. "I will get that done as president of the United States because this is not about policy. This is personal."

But this is about policy, and Booker's initial response was notably lacking in any specifics. He did eventually get around to mentioning, after Todd had asked a different question, that he favors federal licensing of gun owners. "If you need a license to drive a car," Booker said, "you should need a license to buy and own a firearm."

That analogy is not the slam dunk Booker seems to think it is, especially since state governments routinely treat driving on public roads as a "privilege," whereas gun ownership is a constitutional right. Nor is it a credible response to the point that Todd raised, since it would apply only to future gun purchases. And as Brian Doherty notes, the evidence that requiring licenses to buy firearms reduces gun violence, to which Booker alluded, is unpersuasive.

Todd noted that Booker has proposed "a federal government buyback program" and wondered, "How is that going to work?" Booker dodged the question completely, which is not surprising, since the track record for voluntary gun buyback programs is unimpressive. Todd later mentioned "gun confiscation," which would be clearly unconstitutional. No one seemed ready to endorse that idea, although Rep. Eric Swalwell (D-Calif.), who will participate in tonight's debate, supports the confiscation of whatever guns Congress decides to call "assault weapons"—15 million of them, by his estimate.

Former HUD Secretary Julian Castro, who recently told The New York Times that if he had his way "people would not own handguns," called for "common-sense gun reform" without indicating what that would mean.

Rep. Tim Ryan (D-Ohio) recommended "trauma-based care in every school."

Former Texas congressman Beto O'Rourke mentioned "universal background checks," "red flag" laws, and an "assault weapon" ban—the very policy that Todd cited as plainly inadequate to address the "hundreds of millions of guns" already in circulation.

Sen. Amy Klobuchar (D-Minn.) also boasted of her support for an "assault weapon" ban, and she repeated her inane line about evaluating gun control proposals based on whether they would "hurt my Uncle Dick in his deer stand," which betrays a fundamental misunderstanding of the Second Amendment.

New York City Mayor Bill de Blasio said "we want to get these guns off the street," but he also emphasized the need to improve the relationship between police and the communities they serve. "So we need to have a different conversation in this country about guns," he said, "but also a different conversation about policing that brings police and the community together."

De Blasio did not acknowledge the tension between those two goals. His predecessor, Michael Bloomberg, adamantly defended the NYPD's aggressive "stop and frisk" program as a deterrent to young men who might otherwise carry guns. De Blasio rightly opposed that program, which a federal judge deemed unconstitutional and racially discriminatory. But a commitment to "get[ting] these guns off the street" invites tactics like these, which inevitably sour the relationship between cops and the neighborhoods where they routinely detain and search young black and Latino men, frequently for no credible reason. Bloomberg, who continues to defend suspicionless dragnets as a way to "get these guns off the street," is a leading financial backer of the gun control movement.

Former Maryland congressman John Delaney said he has encountered voters who are frustrated by inaction on gun control. He did not provide even a hint as to what sort of action they want.

To be fair, there is no satisfying answer to Todd's question. As long as Americans own hundreds of millions of firearms, any gun control policy Democrats propose will leave plenty of weapons for mass murderers and ordinary criminals, who will easily avoid background checks and gun licensing requirements, no matter what legislation Congress passes. Anything more ambitious would conflict with the Second Amendment. But Democrats want to pretend they have a solution that will "end this crisis by doing the kind of common-sense things that will make our nation safe," as Booker puts it. Regardless of how you feel about guns or the Second Amendment, these are empty promises.