WASHINGTON — When Attorney General William Barr released a redacted version of former special counsel Robert Mueller's report to the public last month, he was asked to explain why it did not reach a conclusion about whether President Donald Trump obstructed justice.

Was it because of the Justice Department's view that a sitting president cannot be indicted?

No, Barr said, adding that during a private meeting in early March, Mueller "made it very clear several times that that was not his position."

But Mueller himself seemed to say the opposite during his public statement on Wednesday. "Under long-standing department policy, a president cannot be charged with a federal crime while he is in office," he said. "Charging the president with a crime was therefore not an option we could consider."

The apparent contradiction has led some to conclude that Barr was suggesting Mueller lacked sufficient evidence to accuse the president of obstruction, while Mueller was saying it was the policy, not the evidence, that prevented him from reaching any such conclusion.

But Justice Department officials and a Mueller associate say the distinction is much more subtle, involving Mueller's own explanation for why the report came out as it did.

When Barr was asked why the report reached no conclusion on the obstruction of justice issue, he used a phrase common among lawyers — "but for," meaning that something would have happened were it not for something else. An example, "I would have made it on time but for the heavy traffic."

Here's what Barr told reporters last month about the March 5 meeting with Mueller and the role played by the Justice Department's position against indicting a sitting president, an opinion written by its Office of Legal Counsel, or OLC: "We specifically asked him about the OLC opinion and whether or not he was taking a position that he would have found a crime but for the existence of the OLC opinion. And he made it clear several times that that was not his position."

"He was not saying that but for the OLC opinion, he would have found a crime. He made it clear that he had not made the determination that there was a crime," Barr said.

Spokespeople for both Barr and Mueller agree that Barr accurately characterized what Mueller said at that meeting. So what explains the apparent difference?

Here's how a Mueller associate explains it. It's true that, as Mueller told Barr, he was not taking a position that "he would have found a crime" were it not for the OLC opinion. That's because the special counsel team never got to the point of deciding whether a crime was committed.

In other words, the OLC opinion prevented the team from even considering whether the president obstructed justice. Mueller therefore told Barr that the OLC opinion didn't stop him from saying a crime was committed. What it stopped was even considering whether the president's actions amounted to a crime.

It's admittedly a very subtle difference. Mueller himself sought to explain the process Wednesday, when he spoke about his two-year investigation for the first time. "We concluded that we would not reach a conclusion one way or the other about whether the president committed a crime," he said.

Neither Mueller nor his associates, however, have offered a public explanation for why the report also said it could not clear Trump on the obstruction issue. "If we had confidence that the president clearly did not commit a crime, we would have said that," Mueller said Wednesday.

Whatever the reason, Mueller himself isn't likely to say. He indicated Wednesday that he has no desire to testify before Congress, saying, "The report is my testimony."

"I would not provide information beyond what is already public in any appearance before Congress," Mueller said.

He formally resigned as special counsel shortly after making his statement at the Justice Department.