Presidential candidates invariably seek and often get endorsements from admired figures in American life. But Hillary Clinton apparently didn’t have to ask to get one of the most noteworthy signals of approval any politician could ask for — a criticism of her likely Republican opponent from a sitting justice of the U.S. Supreme Court.

In an interview with The New York Times, Ruth Bader Ginsburg said, “I can’t imagine what this place would be — I can’t imagine what this country would be — with Donald Trump as our president.” She recalled something her late husband used to say: “Maybe it’s time for us to move to New Zealand.”

The issue here isn’t Trump’s fitness for the presidency — we’re beyond dubious — nor is it Ginsburg’s freedom to think whatever she wishes of him.

But to say her public comments are unusual is like saying dancing cows are scarce. Supreme Court justices don’t — at least until now — take public stands on presidential or other elections. One reason is that they are barred from doing so by the federal code of judicial conduct, which states that as a general rule, judges shall not “publicly endorse or publicly oppose another candidate for public office.” They also aren’t allowed to make speeches on behalf of political organizations or give money to candidates.

The reasons for the ban are clear and sensible. Judges who sit on the federal bench are protected from political pressures by the life tenure provided in the Constitution. Courts are often asked to rule on matters of public controversy, and the litigants on either side are entitled to expect that the presiding judges will evaluate their arguments fairly.

Nowhere is that impartiality more important than in the highest court in the land, which has the final word on a host of grave questions. For justices to descend into partisan election campaigns would undermine public faith in their willingness to assess each case strictly on its legal merits. It would also encourage justices to let their political biases affect, if not determine, their decisions.

Yet here was Ginsburg plainly indicating how she will vote in this election. “I am not aware of any justice ever expressing views on the merits or demerits of a presidential candidate in the midst of the campaign,” Ed Whelan, president of the Ethics and Public Policy Center, told The Washington Post. George Washington University law professor Jonathan Turley told us her comment “showed manifestly bad judgment and undermined the integrity of the Court.”

She is not the first justice to play fast and loose with these obligations. The late Antonin Scalia flew on Dick Cheney’s plane in 2004, when they took a hunting trip together, yet didn’t recuse himself from a suit against the vice president. At an election-watching party in 2000, when it appeared Al Gore had won, Sandra Day O’Connor reportedly said, “This is terrible” — before participating in the decision in Bush v. Gore.

But Ginsburg went even further by publicly stating her opinion of a candidate during a campaign. If Trump is elected, Ginsburg may be expected to rule on the constitutionality or legality of the policies he pursues. Can anyone assume that she’ll put aside her disdain for him and give them a fair hearing? If President Trump were to lose a case, wouldn’t he have plausible grounds to claim, as he often does, “The system is rigged”?

The Supreme Court commands respect and deference from the citizenry partly because it stands outside of petty politics. When a member of the court strides into that muck, she may help a candidate, but she hurts the cause of justice.