“One of the most outrageous — and profoundly misguided — courses of presidential conduct I have witnessed in five decades in and around the nation’s capital,” Starr writes of Trump’s tweets.

Former US Solicitor General Kenneth Starr — who served as the independent counsel in the Clinton administration during the Whitewater and Monica Lewinsky investigations — wrote an op-ed for the Washington Post Wednesday in which he urged President Donald Trump to “stop the wildly inappropriate attacks on the attorney general.”

As Vox’s Andrew Prokop explains, the feud between Trump and his attorney general, Jeff Sessions, is much more than colleagues butting heads — it’s reportedly part of a larger effort by Trump’s team to exert more political control over the Justice Department in an effort to shut down special counsel Robert Mueller’s investigation into ties between Trump’s associates and the Kremlin. Trump has been tweeting his dissatisfaction with Sessions, both for recusing himself from the investigation and for taking “a VERY weak position on Hillary Clinton crimes.”

As the feud has raged on, many have come out in defense of Sessions, but Ken Starr’s op-ed was unexpected. In it, Starr describes Sessions as “[Trump’s] piñata in one of the most outrageous — and profoundly misguided — courses of presidential conduct I have witnessed in five decades in and around the nation’s capital.”

Starr is known for his explosive 1998 report, which attempted to outline a case for the impeachment of President Bill Clinton by detailing his sexual relationship with Monica Lewinsky. In 2010, NPR’s Terry Gross interviewed Ken Gormley, author of Clinton vs. Starr, in a segment looking back at the significance of the investigations. Gormley tells Gross, “It's an event that almost every American remembers and had strong opinions about — like the assassination or the removal of Nixon." Indeed, many still think of Starr as a tenacious, highly-partisan investigator known for, as Gormley says, ushering in “the beginning of the sharp division of red and blue.”

So when Starr took to the pages of the Washington Post to admonish Trump for publicly criticizing Sessions — in particular because Sessions is not opening investigations into Trump’s political opponents — it raised a few eyebrows.

Of the expectations that President Trump and his administration have put on Sessions, and on the role itself, Starr writes:

The attorney general is not — and cannot be — the president’s “hockey goalie,” as new White House Communications Director Anthony Scaramucci described Sessions’s job. In fact, the president isn’t even his client. To the contrary, the attorney general’s client is ultimately “We the People,” and his fidelity has to be not to the president but to the Constitution and other laws of the United States. Indeed, the attorney general’s job, at times, is to tell the president “no” because of the supervening demands of the law. When it comes to dealing with the nation’s top legal officer, you will do well to check your Twitter weapons at the Oval Office door.

On the topic of recusal, he explains why this is necessary:

As a member of the president’s Cabinet, the attorney general needs to be a loyal member of the president’s team, yet at the same time he must have the personal integrity and courage to tell the president what the law demands — and what the law will not permit. That’s especially true with respect to enforcing the nation’s criminal laws, and why — rightly — the attorney general needs to step aside on matters where his own independence of judgment has potentially been compromised.

Specifically on the complicated topic of the idea of the attorney general’s loyalty, he writes:

How to manage the paradox — loyalty to the president leavened by rock-ribbed integrity of judgment? It comes down to courage on the part of the attorney general and a willingness by the president to listen respectfully to what he may well not want to hear.

Starr goes so far as to warn the president directly: “What you are doing is harmful to your presidency and inimical to our foundational commitment as a free people to the rule of law.”