Five weeks ago, special counsel Robert Mueller gave Attorney General William Barr a 448-page report on the Russia investigation. The report documented multiple attempts by President Donald Trump to manipulate, disrupt, and terminate the investigation. But two days after receiving the report, Barr announced that the evidence was insufficient to charge Trump with obstruction of justice.

How did Barr reach that conclusion? On Wednesday, we got the answer: He devised legal standards that make it impossible to convict a president of obstruction.

At Wednesday’s hearing before the Senate Judiciary Committee, Barr testified not as the nation’s chief law enforcement officer but as a defense attorney for the president. When Sen. Amy Klobuchar of Minnesota asked Barr about Trump’s attempts to manipulate witnesses, the attorney general rebutted her by presenting what, in his opinion, “the president’s lawyers would say.” Barr dismissed Mueller’s efforts to get an interview with Trump—Mueller “never sought it. … Well, he never pushed it,” the attorney general lied—and he complained that Mueller’s analysis of the president’s obstructive conduct “permits a lot of selectivity on the part of the prosecutors.”

In place of Mueller’s analysis, Barr laid down four rules that guaranteed Trump would escape prosecution.

1. A president’s efforts to terminate an investigation of himself are presumptively innocent. Under U.S. law, anyone accused of a crime is presumed innocent. But Barr clings to this presumption even after the president has attempted, on multiple occasions, to abort an inquiry into his own alleged misconduct. Barr told the committee that Trump’s presidential orders—including the firing of then–FBI Director James Comey in May 2017 and the attempted firing of Mueller a month later—were “authorized by the Constitution” and therefore “facially innocent.”

2. No amount of evidence can disprove a president’s post hoc account of his motives. Mueller presented copious evidence that Trump, having decided to fire Comey because of the Russia investigation, seized on a completely different rationale—outlined in a memo by Deputy Attorney General Rod Rosenstein—as a pretext for the firing. But at Wednesday’s hearing, when Sen. John Cornyn of Texas asked Barr whether Trump “was relying, at least in part,” on Rosenstein’s critique, the attorney general assured Cornyn, “That’s right.” Mueller also documented conversations in which then–White House counsel Don McGahn and former New Jersey Gov. Chris Christie, an ex-prosecutor, explained to Trump that there were no grounds to fire Mueller based on putative conflicts of interest. But at the hearing, Barr insisted that Trump’s subsequent efforts to oust Mueller might have been based not on fear of the Russia investigation but on the alleged conflicts of interest.

Barr defended the president’s preposterous lie about his attempt, through McGahn, to fire Mueller. In June 2017, Trump’s chief of staff, Reince Priebus, and Trump’s chief strategist, Steve Bannon, said Trump was strongly considering firing Mueller. A few days later, Trump called McGahn twice at home and told him to get rid of the special counsel. According to McGahn, Trump repeatedly pressed him to contact Rosenstein—“Call me back when you do it,” the president told McGahn—and oust the special counsel because “Mueller has to go.” But at Wednesday’s hearing, Barr stood up for Trump’s version of the episode. “What he meant,” said Barr, paraphrasing Trump’s account, “was that the conflict of interest should be raised with Rosenstein, but the decision should be left with Rosenstein.”

Barr was equally generous in his defense of Trump’s signals to witnesses. Klobuchar asked the attorney general about public comments in which Trump had warned two witnesses in the investigation, Michael Cohen and Paul Manafort, not to “flip.” Barr replied that Trump could easily defend those comments. “By flipping, he meant succumbing to pressure in unrelated cases to lie” against the president, Barr suggested. That’s an odd claim to make about Manafort—who was found to have lied to prosecutors while protecting Trump—or Cohen, whose testimony against Trump was corroborated by checks and audio recordings.

3. If a president thinks any part of an allegation is false, he can lawfully obstruct an investigation of that allegation. On Jan. 25, 2018, the New York Times reported Trump’s attempt, through McGahn, to fire Mueller in June 2017. In the week after the Times story appeared, Trump repeatedly pressed McGahn to deny the story. McGahn refused, saying the article was true. Trump rebuked McGahn for taking notes, demanded that he deny the story in writing “for our records,” and threatened to fire him if he didn’t recant.

Mueller documented this episode through White House records and multiple witnesses. But at Wednesday’s hearing, Barr insisted that Trump’s intent was innocent because one word in the Times article was debatable. “The New York Times story said flat-out that the president directed the firing of Mueller,” said Barr. He noted that Trump later denied having used the word “fire” in his calls to McGahn. Therefore, said Barr, it was possible that “the president truly felt that the Times article was inaccurate” and, in ordering his White House counsel to recant, didn’t think “he was instructing McGahn to say something false.”

4. If a president thinks any part of an investigation is unfounded, he can lawfully shut it down. Barr told Sen. Patrick Leahy of Vermont that if a legal proceeding was “based on false allegations, the president does not have to sit there, constitutionally, and allow it to run its course. The president could terminate that proceeding, and it would not be a corrupt intent, because he was being falsely accused.” The attorney general made the same argument to Sen. Dianne Feinstein of California, contending that a “falsely accused” president could fire a special counsel without corrupt intent.

Barr didn’t confine this argument to meritless inquiries. He applied it to investigations that involved any false allegations. He specifically said it was a valid basis for terminating the Russia investigation since the president “was being falsely accused.” “Two years of his administration have been dominated by allegations that have now been proven false,” Barr told the committee. In defiance of Mueller’s report, he claimed that Trump “did nothing wrong” and that suspicions of collusion between Russia and Trump’s campaign were “without a basis.”

Together, Barr’s four rules make an obstruction of justice case impossible. The president could stand in the middle of Fifth Avenue, fire the FBI director, fire a special counsel, threaten witnesses, and instruct subordinates to lie, and he wouldn’t lose the support of his attorney general. That’s why Trump hired Barr in the first place. And that’s why Mueller’s investigation shouldn’t end with Barr’s refusal to prosecute the president. We can’t let a lawyer acquit his own client.