Is the liberal wing of the Supreme Court embracing the cause, associated with conservatives, of judicial restraint? That’s the question after Justice Ketanji Brown Jackson scolded the court majority for intervening in the case of a Maine state lawmaker who was muzzled by her colleagues for traversing left-wing orthodoxy on transgender issues. The high court jumped in to overturn the lawmaker’s punishment while the case plays out in lower courts.

The rhubarb arose when a Republican representative in the Pine Tree State, Laurel Libby, took to social media to decry the participation of transgender athletes in girls’ athletics. Ms. Libby’s post included photographs and the name of a transgender female high school student who had won a pole-vaulting competition. While Ms. Libby stresses her free speech rights, she sparked criticism for posting online information about a minor.

Ms. Libby’s social media post “earned her a formal censure by her colleagues in the Maine House of Representatives,” Judge Melissa DuBose explained, and a “sanction prohibiting her from speaking or voting on the House floor until she apologizes for her post.” The lawmaker, though, is standing firm. She contends that the punishment meted out by Maine’s house — barring her votes from being counted — denies her constituents a legislative voice.

That argument brings federalism to the center of what might otherwise seem like a free speech controversy. After all, Maine’s house speaker, Ryan Fecteau, insisted to the Nine that “the power of a legislative body to punish its members has been recognized in the common law since ancient times.” Plus, too, he explains, this right “has been enshrined in the U.S. Constitution and many state constitutions, including Maine’s, since the birth of our republic.”

Mr. Fecteau reckons that Ms. Libby’s punishment stems from her having “targeted a Maine high-school student on social media.” He notes that she “was found by a majority of her fellow Maine House members to have breached Maine’s Legislative Code of Ethics.” Yet Ms. Libby calls it “a remarkable break from history” to allow Maine’s house to allow the “disenfranchisement of thousands” of her constituents over their “representative’s protected speech.”

Lower courts ruled against Ms. Libby, prompting her plea to the Supreme Court to restore her voting and speaking privileges in the Maine house while the dispute is pending. Justice Jackson rebuked the majority’s move in a dissenting statement that relied in part on legal reasoning from a colleague, Justice Amy Coney Barrett, our A.R. Hoffman reports. Why, Justice Jackson asks, was the majority in such an all-fired rush to step in on Ms. Libby’s behalf?

Such a move by the Nine — in effect short-circuiting the litigation in the lower courts — is typically undertaken only when “critical and exigent circumstances” warrant the “intervention,” Justice Jackson avers. She finds that the First Circuit “is moving quickly to evaluate the legal issues,” and that there are no “significant legislative votes scheduled in the upcoming weeks.” She sees no risk of “any concrete, imminent, and significant harm” to Ms. Libby.

Justice Jackson frets, too, that the early intervention in Ms. Libby’s case ends up “creating perverse incentives to seek our intervention prematurely.” She voices nostalgia for the days when “this Court treaded carefully with respect to exercising its equitable power” to issue orders in “an emergency.” Is she suggesting that courts should be more circumspect before plunging ahead with, say, the sweeping national injunctions that have crimped President Trump’s agenda? 

Or is Justice Jackson merely cloaking her opposition to Ms. Libby’s views with the mantle of procedural principle? During her Senate confirmation hearings, after all, the justice declined to define a “woman.” Quoth she: “I’m not a biologist.” Either way, Justice Jackson concedes that the dispute “raises many difficult questions” relating to constitutional rights and federalism. On that head, one imagines the high bench is unanimous.