Senior Judge Michael Ponsor criticized Alito in an essay for the New York Times, blasting the Supreme Court justice for flying an upside-down American flag outside his home in Virginia and a Revolutionary War-era “Appeal to Heaven” flag outside his beach home. Democrats complained that the flags were an indication of Alito’s bias toward Republicans and demanded he recuse himself from cases involving President-elect Donald Trump that were before the court.

Ponsor, a judge in the U.S. District Court for the District of Massachusetts, an appointee of former President Bill Clinton who took the court in 1994, wrote that Alito’s decision to fly the flags was “improper” and “dumb” in a surprising broadside as federal judges rarely criticize other judges publicly, especially not Supreme Court justices.

“Courts work because people trust judges. Taking sides in this way erodes that trust,” Ponsor wrote in the piece, which accused Alito of hurting trust in the high court. “You just don’t do that sort of thing, whether it may be considered over the line, or just edging up to the margin. Flying those flags was tantamount to sticking a “Stop the steal” bumper sticker on your car. You just don’t do it.”

However, an investigation by Chief Judge Albert Diaz of the U.S. Court of Appeals for the 4th Circuit, an appointee of former President Barack Obama, after a complaint about the essay was filed found Ponsor had violated rules and harmed “public confidence in the integrity and impartiality of the judiciary.”

Diaz found the essay eroded the “public’s confidence in the integrity and independence of the judiciary” and could “reasonably be viewed as a commentary on partisan issues.”

The complaint about Ponsor’s essay said the senior judge’s comments were “highly inappropriate, baseless, and prejudicial political speech by a judge against another judge while he is deciding the legal fates of criminal defendants going through the judicial process.”

Ponsor wasn’t punished for his essay after he apologized for the essay and acknowledged it had “violated the boundaries of our Code of Conduct.”

“With the benefit of an objective perspective, I realize now that my criticism of the ethical judgement of a Supreme Court Justice might have had the effect of undermining the public’s confidence in the integrity of the judicial system,” Ponsor said in his apology.

“For these violations of the Code, unintentional at the time but clear in retrospect, I offer my unreserved apology and my commitment to scrupulously avoid any such transgression in the future,” the senior judge added.

The Alito-flag saga was part of a stream of criticisms by Democrats in recent years over the Republican-majority Supreme Court. Senate Democrats, who expressed their displeasure with the Alito flag reports, have also pushed for reforms to the ethics code over reports of undisclosed gifts given to justices in recent years.