After publicly criticizing President Donald Trump's habitual commentary on federal criminal cases, Attorney General William Barr reportedly is threatening to resign if it continues. Trump, meanwhile, not only shows no sign of heeding Barr's admonition; he does not seem to understand the concerns that motivated it. In fact, Trump thinks he has shown remarkable restraint.

"I chose not to be involved," the president told reporters yesterday, referring to the revised sentencing recommendation for longtime Trump crony Roger Stone. "I'm allowed to be totally involved. I'm actually, I guess, the chief law enforcement officer of the country, but I've chosen not to be involved."

The attorney general is usually described as the federal government's "chief law enforcement officer"—a designation endorsed by the White House as well as the Justice Department. But Trump is alluding to the argument that the president, who is in charge of the executive branch and has a constitutional duty to "take care that the laws be faithfully executed," is the ultimate wielder of that power. Barr, after all, answers to Trump, not the other way around. If Trump does not like the way Barr is running the Justice Department, he can always replace him with someone else.

But can is not the same as should—a distinction that seems to elude Trump. It would be one thing if Trump fired Barr because he thought the attorney general was doing a poor job of implementing the administration's policies. It would be another thing if Barr got the boot because Trump thought the Justice Department should stop prosecuting his friends and start prosecuting his enemies.

Both decisions are within Trump's power, but the latter is an abuse of his power, because faithful execution of the laws precludes using them to grant favors and exact revenge. This is precisely the sort of banana-republic corruption that people had in mind during the impeachment debate when they rejected the idea that Congress can remove the president only if he violates a criminal statute.

When it comes to presidential meddling in criminal cases, appearances matter. The president should not undermine the rule of law by ordering the Justice Department to make prosecutorial decisions based on his own personal or political interests. Nor should he undermine public confidence in the rule of law by making it look like he is giving such instructions. Those norms help protect the Justice Department's independence, which in turn helps protect all of us from the whims of a vindictive president.

Speaking of appearances, Barr overrode the initial sentencing recommendation for Stone, which called for a prison term of seven to nine years, after Trump condemned it as "horrible and unfair." The amended sentencing memorandum recommends "a sentence of incarceration far less" than the one originally proposed. Barr says he decided to file the new memorandum before Trump's tweet, based on his own view of what was "fair and reasonable in this particular case," rather than the president's personal objections. Whether or not you buy that, Barr clearly believes the distinction is important, while Trump does not get what all the fuss is about.

Trump calls Barr "a straight shooter" and "a man with great integrity" but does not seem to understand what that means. "I do make his job harder," he acknowledged yesterday, and he plans to continue doing so. "Social media, for me, has been very important because it gives me a voice, because I don't get that voice in the press. In the media, I don't get that voice."

Leaving aside the risible claim that the world's most powerful politician has trouble getting his message across, Trump's insistence on expressing his opinions about which criminal cases federal prosecutors should and should not pursue reflects not just his notorious lack of discretion but his disdain for the very idea that justice should be blind. While that goal may always be more of an aspiration than a reality, Trump does not even seem to think it is worth pursuing.

"I am not supposed to be involved with the Justice Department," Trump complained in a 2017 radio interview. "I'm not supposed to be involved with the FBI. I'm not supposed to be doing the kind of things I would love to be doing, and I am very frustrated by it." After more than three years in office, Trump remains frankly puzzled by the notion that he should restrain himself to protect the integrity of the criminal justice system.