A big question hanging over William P. Barr’s nomination to be attorney general this year was whether, once he got the job, he would do President Trump’s bidding. Barr had made statements critical of special counsel Robert S. Mueller III’s investigation, and he even wrote a long memo rejecting the need for the obstruction of justice portion of Mueller’s inquiry. Trump also repeatedly made clear his desire for a loyalist to oversee the investigation.

On Sunday, Barr made a big decision in Trump’s favor. And he did so in a way legal experts say is very questionable.

In his four-page letter describing the report’s major findings, Barr noted that Mueller didn’t conclude that Trump committed obstruction of justice but that Mueller also said, pointedly, that he wasn’t exonerating Trump either.

Then Barr stepped forward to offer his own exoneration.

“After reviewing the Special Counsel’s final report on these issues; consulting with Department officials, including the Office of Legal Counsel; and applying the principles of federal prosecution that guide our charging decisions,” Barr wrote, “Deputy Attorney General Rod J. Rosenstein and I have concluded that the evidence developed during the Special Counsel’s investigation is not sufficient to establish that the President committed an obstruction-of-justice offense.”

He further explained. “In making this determination, we noted that the Special Counsel recognized that ‘the evidence does not establish that the President was involved in an underlying crime related to Russian election interference,’ and that, while not determinative, the absence of such evidence bears upon the President’s intent with respect to obstruction.”

There are a few reasons this conclusion is problematic.

The first is Barr’s rationale. Legal experts say it’s odd that he emphasized the lack of an underlying, proven crime, given that’s not necessary for obstruction of justice.

“I think this is the weakest part of Attorney General Barr’s conclusions,” said Jessica Levinson, a professor at Loyola Law School in Los Angeles. “You do not need to prove an underlying crime to prove obstruction of justice. Martha Stewart is quite aware of this fact.”

“For example,” added former federal prosecutor David Alan Sklansky, now of Stanford University, “if the President wrongfully tried to block the investigation into Russian interference in the election because he wanted to protect the Russians, or because he didn’t want people to know that a foreign government had tried to hack the election in his favor, that would constitute obstruction.”

Gene Rossi, another former federal prosecutor, said the lack of an underlying crime does matter. “However, the existence of an underlying crime is not an essential element of the crime of obstruction. End of story,” he said. “To the extent the attorney general suggests such an element, he is dead wrong.”

It’s important to note that Barr doesn’t quite say this means there can’t be obstruction of justice, but it is a point of emphasis.

But even then, is it really true? Although Mueller determined that there was no evidence of collusion between the Trump campaign and Russia, he was able to charge and prove other crimes by Trump associates. Former national security adviser Michael T. Flynn pleaded guilty to lying to the FBI about his contacts with the Russian ambassador to the United States, and Trump allegedly requested that then-FBI Director James B. Comey be lenient on Flynn. That’s an actual crime Trump could be trying to cover up.

The same goes for longtime Trump adviser Roger Stone, who has been indicted in connection with attempts to contact WikiLeaks during the 2016 campaign. Stone’s indictment notably said that “a senior Trump Campaign official was directed to contact STONE” about the matter. Some have suggested that it might be Trump who did that directing. Even if it wasn’t, Mueller clearly sees an actual crime here, which Trump’s actions vis-a-vis his investigation could affect.

Trump campaign chairman Paul Manafort was sentenced to 7½ years in prison. Former Trump lawyer and fixer Michael Cohen got three. Cohen has implicated Trump in Cohen’s felony campaign finance violations, and Trump has engaged in very public conduct that some have alleged was meant to intimidate Cohen as he testified before Congress.

Barr’s argument is that the lack of an underlying crime suggests there’s less reason to believe Trump had a “corrupt intent” behind his actions regarding the investigation. But if you set aside collusion, there would seem to be plenty for Trump to want to cover up. Even if these proven and alleged crimes didn’t involve criminal activity by Trump personally, he would seem to have a clear interest in the outcomes of these investigations, both because of his sensitivity about the idea that Russia assisted him and because of the narrative it created of a president surrounded by corruption.

“You don’t need to be guilty of an underlying crime to obstruct an investigation — especially one that might, and in fact did, implicate a number of close associates and aides,” said Jens David Ohlin, a law professor at Cornell University.

And the last point is that this is not a determination Barr necessarily needed to make. Justice Department guidelines say that a sitting president can’t be indicted, so as attorney general, Barr’s conclusions about Mueller’s report weren’t really needed. Congress is the ultimate arbiter here, through potential impeachment proceedings. The fact that Mueller opted not to make a specific recommendation on obstruction of justice may have convinced Barr to weigh in, but he could have just left it at Mueller opting not to accuse Trump of a crime.

Instead, Barr made a determination based on reviewing Mueller’s report for less than 48 hours. In doing so, he invited Democrats to accuse him of going above and beyond for the man who appointed him — and who had, for months and months before then, very publicly resented the fact that his previous attorney general, Jeff Sessions, had recused himself from the investigation.

Ultimately, Congress will make its own determinations, and Democrats have signaled that they are not going to let this lie. But Barr’s statement is an important one when it comes to whether Republicans would ever go along with impeaching or removing Trump — and whether voters might support Trump in 2020.

This is what Barr’s critics feared when the Senate voted to confirm him two months ago. It’s why they urged him to recuse himself from the Russia investigation. And it’s going to be a significant point of contention in the hours and days ahead.