The Supreme Court as we once knew it—as a national institution that could at least sometimes stand apart from partisanship—died last year. The ongoing fight over its corpse spilled into public view last week.

On Thursday, 53 United States senators—every member of the Republican caucus—wrote a “letter” to the clerk of the Supreme Court assuring the justices that the Republican Party has their back. The Democrats, the senators told the Court, pose “a direct, immediate threat to the independence of the judiciary.”

The spat is about guns. The Court has granted review in a Second Amendment case entitled New York State Rifle & Pistol Association Inc. v. City of New York, New York, which (nominally) tests an obscure New York City ordinance governing how firearms owners could—note the past tense—travel with their weapons.

Under city law as it was when the case began, New Yorkers with a “premises” license had to keep their guns in their homes at all times, except when being taken to a licensed target-shooting facility for practice and training. But those facilities had to be in New York City itself. “Premises” licensees could not put their guns in their trunk and drive out of town for any reason—not to go to a gun range, not to compete in a shooting match, not to take the guns to a second home.