“Hell, yes,” former Texas Congressman Beto O’Rourke said triumphantly from the Democratic debate stage, “we’re going to take your AR-15, your AK-47.” It was a line made for a t-shirt, which is precisely where it ended up. Depending on your view of gun rights, O’Rourke’s declaration was either a masterful effort to thrust open the Overton Window or an attack on decades of carefully crafted Democratic messaging on the issue of guns. To gauge it by Joe Biden’s latest proposal on guns, both assessments are true. What constitutes acceptable gun policy among Democrats has become broader, but what remains politically viable has not.

On Wednesday, the former vice president rolled out a plan to curb assault-style rifles by banning their distribution and manufacture (as well as that of high-capacity magazines)—essentially, reinstating the 1994 Assault Weapons Ban. According to Axios’s summary of the forthcoming proposal, though, Biden stops short of endorsing an O’Rourke-style mandatory buyback program for semi-automatic rifles already in private hands. “Instead,” it reads, “it gives those who own such guns two choices: sell the weapons to the government or register them under the National Firearms Act.”

There’s just one problem: The National Firearms Act doesn’t provide for a national gun registry. Indeed, the law expressly prohibits the federal government from establishing a “system of registration of firearms, firearms owners, or firearms transactions or disposition.” The Manchin-Toomey background-check legislation that failed in the U.S. Senate in 2013 also contained an amendment expressly outlawing a federal gun registry—again, just for good measure. Biden’s proposal acknowledges that such a registry does not yet exist, but it does not expand on why. If it did, his proposal would be exposed for what it is: a non-starter.

Why is there so much opposition to a federal gun registry in American law? In part, because the politics of the issue favor gun owners, who are vehemently opposed to such a provision and fear that it could one day be used by the federal government to deem certain guns illegal retroactively and to confiscate them. Biden’s proposal, to say nothing of O’Rourke’s, confirms the validity of those concerns. More important, however, a federal registry is not effective policy.

Canada’s experience is illustrative. As Vincent Harinam and Gary Mauser demonstrate in National Review, the Canadian effort to impose a national licensing regime on its comparatively small population of gun owners was a failure. “It took the Canadian government six years to implement the 1995 legislation with fewer than 2 million gun owners signing up for licenses as of 2001,” they wrote. “Worse yet, the RCMP later reported error rates of 43 to 90 percent in firearm applications and registry information.” Over 4,400 stolen weapons were successfully registered with federal authorities. The cost of the program ballooned by more than 1,000 percent. It had no impact on gun-related murder rates, which increased over the life of the program. And, by 2012, a national gun registry was terminated.

When asked how Biden would overcome the aversion in Congress toward some of his proposals to restrict gun ownership, a campaign aide replied, “You have in the vice president’s record two examples of him succeeding in getting legislation done and defeating the NRA before.” That record does not extend to the Manchin-Toomey bill, a vote over which he presided in the Senate and that failed with five Democratic defections. The Democratic caucus that controlled the Senate in 2013 was geographically broader than the president Democratic minority and, thus, less ideologically doctrinaire. If the Democrats regain control of the Senate, their majority would likely be just as ideologically heterogeneous. It is unclear how legislation with fewer protections for gun owners would sail through that chamber given how past efforts along these lines performed.

The chief value proposition in Biden’s proposal isn’t its viability as a blueprint for legislation but that it positions him more to the left of his party on the issue of guns. But Biden is trying to have it both ways. By endorsing a plan that establishes a backdoor confiscatory regime for assault-style weapons without explicitly calling for such a regime, he risks alienating both gun-rights voters and Democrats for whom no gun safety measure is too extreme. If these are Biden’s best political instincts, you’d hate to see his worst.