A little rusty, but as yet serviceable — that, in the shell of a nut, seems to be the Supreme Court’s view of the Alien Enemies Act, described by these columns as a “226-Year-Old Sword.” President Trump is wielding the law to deport Venezuelan gang members. The Nine on Monday cleared the way for the law’s application, for now, despite efforts by a lower court judge to halt the deportations. The dispute, though, is far from settled with Monday’s decision.

That’s in part because the high court’s opinion is limited in its scope. It is by no means a comprehensive review of the 18th-century Alien Enemies Act’s application to current affairs. The court’s majority was focused instead on a district court judge’s halt on the law’s use. That block, a temporary restraining order, was imposed by a district court judge, James Boasberg, whom Mr. Trump has derided as a “Radical Left Lunatic.”

We bear no grudge, per se, against Judge Boasberg, though it would seem that the high court’s move on Monday offers little vindication for his handling of the case. The majority holds that the detainees in the dispute erred by filing their case in court at Washington, D.C., as opposed to Texas, where they are being held. The majority also held that the detainees need to challenge the legality of their detention before making other claims.

The detainees, the Nine say, “challenge the Government’s interpretation” of the Alien Enemies Act and “assert that they do not fall within the category of removable alien enemies.” The high court majority says that, at this stage of the case, it does “not reach those arguments.” That’s because “challenges to removal under” the Act “must be brought” via what’s known as a writ of habeas corpus — a claim that the government is illegally confining someone.

As for the Act itself, the majority avers, it “largely ‘preclude[s] judicial review,’” a precedent from the case of Ludecke v. Watkins. In that case, the Supreme Court in 1948 affirmed the president’s authority to expel a foreign national — Kurt Ludecke, an ardent Nazi — without much oversight from the courts. Even the question of whether a war was afoot, which activates the president’s power under the Act, was not for judges to evaluate, per Ludecke.

From the judicial beyond, Justice Felix Frankfurter could derive some satisfaction to find his majority opinion in Ludecke cited by his successors. His opinion, we have noted, amounted to “a paean to judicial modesty.” The jurist wrote that while the president’s “war powers may be abused,” that “is a bad reason for having judges supervise their exercise, whatever the legal formulas within which such supervision would nominally be confined.”

Monday’s decision is not an unalloyed victory for Mr. Trump’s Justice Department. The majority concedes the due process rights of the detainees, even though “judicial review under the AEA is limited.” They add that any “individual subject to detention and removal” under the Act is owed court review of the law’s “interpretation and constitutionality,” and of whether he or she “is in fact an alien enemy fourteen years of age or older.” 

So, the majority says, the detainees “are entitled to notice and an opportunity to challenge their removal,” and the “only question is which court will resolve that challenge.” The dissent by the court’s three liberal justices, joined in part by Justice Amy Coney Barrett, stresses concerns about “scores of Venezuelan immigrants detained in the United States” having been removed “to a foreign prison in El Salvador” without, they say, “any due process of law.”

The dissent, written by Justice Sonia Sotomayor, takes exception to what she calls Mr. Trump’s “unprecedented peacetime invocation of a wartime law.” Yet Mr. Trump reckons that the Venezuelan-tied Tren de Aragua gang “is perpetrating, attempting, and threatening an invasion or predatory incursion against” America. Will courts uphold Mr. Trump’s finding or will he have to sheathe his antique sword are questions yet to be resolved.