Supreme Court Justice Clarence Thomas waded into the post- ­Parkland debate on Tuesday — with an opinion denouncing what he sees as the high court’s insufficient support for the right to keep and bear arms.

The lower federal courts, Thomas charged, have been guilty of a “general failure to afford the Second Amendment the respect due an enumerated constitutional right,” and the Supreme Court, by failing to check this trend, is treating the Second Amendment as “a disfavored right.” The latest example, Thomas protested, was the court’s refusal to hear an appeal by Californians who already own guns but seek to overturn that state’s 10-day waiting period to buy more.

Jarring as his words sounded at this moment, Thomas’s timing reflected the quirks of the court’s schedule rather than anything deliberate on his part.

Still, the juxtaposition is a stark reminder of two realities: First, survivors of the massacre in Florida and other gun-control advocates are up against a powerful movement; second, even if the Parkland shootings lead to tougher laws — state or federal — the final word could belong to the Supreme Court.

A decade ago, the justices handed the gun-rights movement a historic victory, declaring by a 5-to-4 vote in District of Columbia v. Heller that the Second Amendment protects an individual’s right to firearm possession.

Like other constitutional rights, this one was not unlimited; the court said there might be room for “prohibitions on the possession of firearms by felons and the mentally ill,” or laws forbidding the carrying of firearms in schools or government buildings.

This obviously left a lot unresolved. Is there a constitutional right to bear arms for self-defense outside the home? By what standard, exactly, should federal courts decide whether any particular gun law is constitutional?

Opinion | The Washington Post Editorial Board appeals to Trump and Congress to stand up to the gun lobby and prevent mass shootings. (The Washington Post)

For the most part, however, the justices have allowed lower federal courts to fill in those blanks. And those courts, in turn, have generally interpreted Heller as permitting state and local gun regulations. One exception came in 2016, when the Supreme Court summarily vacated a ruling by Massachusetts’s highest court upholding that state’s ban on nonlethal stun guns.

The Supreme Court’s reluctance to weigh in again reflects the fact that, generally, only blue states enact restrictive laws in the first place. There are consequently few conflicts among the regional circuit courts of appeal for the justices to settle.

In practical terms, this means that the states — red and blue — have been free to pursue their separate approaches, as long as no one tries to prohibit gun (or stun-gun) ownership outright.

There’s a certain rough wisdom to that. What Thomas wants, though, is for the Supreme Court to rein in the lower courts — to nationalize a broad individual right to own guns and to require that any limitations face heightened judicial scrutiny, just as, say, restrictions on speech must do.

“If a lower court treated another right so cavalierly,” he complained in the opinion, “I have little doubt that this Court would intervene.”

And he has half a point. Having placed the right to gun possession on the same plane as the other Bill of Rights guarantees, it is a trifle inconsistent for the justices to leave the precise definition of that right to others.

Obviously — painfully so, after Parkland, and Las Vegas, and Newtown — guns present unique dangers, as the court acknowledged in Heller.

Yet that argues for more guidance from the institution that produced that opinion as to what regulations the Constitution does and does not allow, not less.

Four justices must vote to hear a case; though only Thomas affixed his name to Tuesday’s opinion, he is probably not alone in his views. Justice Samuel A. Alito Jr. wrote a vigorous denunciation of the Massachusetts stun-gun ban in 2016, and Justice Neil M. Gorsuch joined Thomas last year when the latter dissented from the court’s refusal to hear a challenge to California’s ban on carrying a loaded handgun in public.

Thomas seems unable to persuade the court’s other two conservatives, Chief Justice John G. Roberts Jr. and Justice Anthony M. Kennedy, to join his project. Like Thomas, both voted with the majority in Heller; unlike him, perhaps, they are not eager to engage in repeated constitutional analyses of blue-state gun laws, each case potentially more politically fraught than the last.

A change in the Supreme Court’s hands-off approach may require a change in Supreme Court personnel. The current lineup can’t last forever.

Kennedy is 81 and just completed his 30th year on the court. Justice Ruth Bader Ginsburg, a dissenter in Heller, is 84 . If either leaves before 2021, President Trump — “The right to keep and bear arms protects all our other rights,” he said in 2016 — would nominate the replacement.

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