A Democratic congressman “went there” Thursday.

In an editorial in USA Today, Rep. Eric Swalwell proposed a mandatory buyback of all “military-style semiautomatic assault weapons” without any “grandfather clause” for existing weapons or any deference to the Second Amendment — the sort of forced-confiscation plan that gun-rights advocates have warned about and gun-controllers have hotly denied they seek.

The California Democrat called reinstating the federal assault-weapons ban from the 1990s a good beginning, “but it would not affect weapons already possessed.”

“Instead, we should ban possession of military-style semiautomatic assault weapons, we should buy back such weapons from all who choose to abide by the law, and we should criminally prosecute any who choose to defy it by keeping their weapons,” Mr. Swalwell said.

In 2016, Democratic presidential nominee Hillary Clinton spoke approvingly at a town-hall meeting of Australia’s gun-buyback program in the wake of a massacre in which a gunman killed 35 people with an assault weapon.

When the NRA pointed out that Australia’s program was not voluntary, as many U.S. cities and states have offered, but a mandatory confiscation, her campaign issued a statement saying she “does not support national mandatory gun buyback programs, including those modeled after Australia’s program.”

Kris Brown, co-president of the Brady Campaign, has repudiated confiscation, telling NBC News in March that “it’s about keeping guns out of dangerous hands and not about confiscating guns.”

No such waffling for Mr. Swallwell — “Australia got it right,” he wrote.

Mr. Swallwell also downplayed the Second Amendment implications of mandatory gun confiscation, in part by saying that even late Justice Antonin Scalia in the Heller decision wrote that the right to keep and bear arms is not unlimited.

But he also implied that it wouldn’t matter anyway because gun control saves lives, which matters more than individual rights.

The students from the latest school shooting in Parkland, Fla., he wrote approvingly, “dismiss the moral equivalence we’ve made for far too long regarding the Second Amendment. I’ve been guilty of it myself, telling constituents and reporters that ‘we can protect the Second Amendment and protect lives.’

“The Parkland teens have taught us there is no right more important than every student’s right to come home after class. The right to live is supreme over any other,” Mr. Swalwell wrote.

Mr. Swalwell is not a marginal back-bencher; the USA Today column identified him as a co-chairman of the House Democratic Steering and Policy Committee, and a member of the House Judiciary Committee.