It took special counsel Robert S. Mueller III nearly two years to conclude that President Trump may have — but may not have — obstructed justice. It took Attorney General William P. Barr and his deputy, Rod J. Rosenstein, only two days to decide that Trump should not be charged with obstruction. How did Barr and Rosenstein make up their minds so quickly on a question that the special counsel struggled with for so long?

Barr sent a letter to Congress on Sunday that offers little explanation for the decision not to prosecute the president. The letter correctly states the elements of obstruction of justice — corrupt intent, obstructive conduct and a sufficient nexus to a pending or contemplated proceeding — and then states that Mueller’s report “identifies no actions that, in our judgment,” satisfy all three criteria. The letter says nothing more about the last two elements of obstruction, but it does offer this about corrupt intent: “While not determinative, the absence of … evidence [of collusion] bears upon the President’s intent with respect to obstruction.”

That conclusion is questionable for reasons beyond its haste. It’s black letter law that a defendant can satisfy the corrupt intent criterion for obstruction even if the defendant himself committed no underlying crime. For example, the U.S. Court of Appeals for the 3rd Circuit recently ruled that a defendant could be convicted of obstruction “even if [his] primary motivation was to extricate the sister of his childhood friend from a troubled situation.” A court in Utah held in 2013 that a defendant could be liable for obstruction where his only apparent motive was to protect a friend from a criminal charge.

Former Detroit mayor Kwame M. Kilpatrick went to jail for obstructing justice in 2008 after he lied under oath about an extramarital affair. And in January, a Navy captain in Florida was indicted on a charge of obstruction of justice after he allegedly misled investigators about his extramarital affair with a civilian employee’s spouse. Of course, adultery is not a crime. But interfering with an investigation to cover up adultery certainly is.

By these standards, it’s easy to see what possible motives Trump may have had to obstruct justice, even if no collusion with Russia was involved. He may have wanted, for example, to shield Michael T. Flynn, his first national security adviser, from criminal liability. In February 2017, the president told FBI Director James B. Comey that Flynn “is a good guy,” according to Comey, and Trump implored Comey to drop the FBI’s investigation of Flynn. Flynn later pleaded guilty to charges that he lied to investigators about his conversations with the Russian ambassador. Trump fired Comey in May 2017.

Or perhaps the president suspected — correctly — that the investigation of his longtime personal attorney Michael Cohen would churn up evidence that Trump paid adult-film actress Stormy Daniels to stay quiet about an alleged sexual encounter the two had just months after Trump’s wife, Melania, gave birth to Trump’s youngest child, Barron. Trump may have feared the political fallout from revelations that he lied to the American people about his business dealings with Russia, and then instructed his eldest son, Donald Trump Jr., to lie about conversations with Russian representatives during the 2016 presidential campaign.

Or maybe Trump simply wanted to cover up the fact that the Russian government intervened on his behalf during the race — even if that intervention occurred independently of Trump’s campaign. Trump has only begrudgingly acknowledged that the intelligence community agrees that Russia wanted him to win; ever sensitive about his loss to Democrat Hillary Clinton in the popular vote, perhaps he worried that evidence of Russian meddling would cast further doubt on the legitimacy of his presidency.

Of course, the fact that Trump would have had many motives to obstruct justice doesn’t mean that he actually did so. Obstruction of justice still requires two more elements beyond corrupt intent: obstructive conduct and a sufficient connection to a pending or contemplated proceeding. The second element — obstructive conduct — is arguably the most difficult to establish in Trump’s case. Reasonable minds may disagree as to whether the president engaged in obstructive conduct when he fired Comey, tried to fire Mueller and possibly encouraged Cohen to lie to Congress, as Cohen has testified. (Trump has repeatedly said Cohen is lying now.)

Trump or his defenders could argue, for example, that he fired Comey not to interfere in an investigation but because he concluded, as he wrote in his termination letter, that Comey was “not able to effectively lead the Bureau.” Comments that Trump made later to NBC News’s Lester Holt undermined that explanation, but if charges had been brought, a jury may have concluded that Trump lied to Holt and told the truth in his earlier termination message.

So why did Barr emphasize the absence of collusion — a fact that is, at most, tangentially relevant to whether Trump obstructed justice?

One possibility is that Mueller’s report contains additional evidence of obstructive conduct connected with a contemplated or pending proceeding. What initially looks like the weaker elements of the obstruction case against Trump may be stronger than we think.

A less conspiratorial theory is that Barr simply has an idiosyncratic view of obstruction — a view that appears to be unmoored from any case law. In his June 2018 memo to top Justice Department officials, Barr — who at the time was a lawyer in private practice — opined that “the President’s motive in removing Comey and commenting on Flynn could not have been ‘corrupt’ unless the President and his campaign were actually guilty of illegal collusion.”

Barr’s view was silly then and is silly now.

Even if Trump’s only motive for interfering in the FBI’s investigation of Flynn was his personal affection for a loyal aide, the president still could have committed obstruction of justice — friendship, as mentioned above, is motive enough for obstruction. Barr’s memo was roundly criticized in December when the Wall Street Journal first reported its existence. Perhaps that criticism led Barr to double down on his strange and legally unsupportable theory.

Ultimately, understanding what is going on in Barr’s mind may be as difficult as understanding what’s happening in Trump’s. It’s hard to see why the attorney general would put so much weight on such a legally flimsy reed. But this much seems clear: Barr’s conclusion that Trump did not commit obstruction should persuade no one of the president’s innocence.