In 1991, then-Attorney General William P. Barr holds a news conference with his assistant attorney general at the time, Robert S. Mueller III. (Barry Thumma/AP)

In his report into Russian interference in the 2016 election, special counsel Robert S. Mueller III cites instance after instance of President Trump pushing to end the investigation, scale back its scope and influence witnesses involved in the probe — all with an intent that could amount to criminal obstruction of justice.

But the special counsel’s team stopped short of accusing the president of this crime, in part because it did not believe it had the legal authority to do so.

Attorney General William P. Barr did not feel so inhibited and definitively declared that the president hadn’t obstructed justice. He went so far as to suggest during a Thursday morning news conference before the report was released that the president’s actions were understandable because he was upset that the investigation and the attention it received were undermining his presidency.

“There is substantial evidence to show that the president was frustrated and angered by a sincere belief that the investigation was undermining his presidency, propelled by his political opponents, and fueled by illegal leaks,” he told reporters.

The gap between Mueller and Barr — both about what the law allows and their conclusions on obstruction — immediately stoked a debate over how to address a sitting president engaging in impropriety and possibly in criminal conduct.

On one side are those who agree with Barr — if Trump wasn’t guilty of conspiring with Russians, it’s hard to prove he had criminal intent in trying to thwart that investigation. On the other side are those who look at the exhaustive evidence laid out in the Mueller report and ask: If this is not obstruction, what is?

David Alan Sklansky, a Stanford law professor and expert on prosecutorial restraint, said Mueller tried to carefully thread the needle in his complex assignment — laying out evidence without assessing its criminality. But he created a dangerous vacuum.

“It was a tough call,” Sklansky said. “But it created an opening for the attorney general — only because the attorney general misrepresented what the special counsel had said.”

Sklansky argued that Barr has left the impression with the public that Mueller believed it was too difficult to reach a conclusion on whether Trump obstructed justice when the report shows the special counsel’s office believed it was its job to investigate the issue and leave it to Congress to act.

Current and former officials said tensions have grown inside the Justice Department since Mueller submitted his report without a conclusion, a decision Barr and some of his top advisers strongly disagree with because they believe it is a core responsibility of prosecutors to reach a decision, even when investigating the president.

Mueller felt bound to follow two Justice Department legal opinions, from 1973 and 2000, that found prosecutors couldn’t prosecute a sitting president. The special counsel concluded those opinions also meant he couldn’t even reach the threshold question of deciding whether Trump had engaged in a crime, according to people familiar with the prosecutors’ thinking who requested anonymity to describe their private deliberations.

Mueller’s team disagreed with many of Barr’s claims about the probe, the report shows. The prosecutors wrote that they should investigate whether a president, despite his broad constitutional powers, had tried to corrupt the criminal justice system. Someone can be charged with obstruction by trying to thwart a probe, but does not have to be successful in their efforts, they argued.

The special counsel’s team noted that Trump often was unsuccessful in his efforts “largely because the persons who surrounded the president declined to carry out orders or accede to his requests.”

Chuck Rosenberg, a former U.S. Attorney in the Eastern District of Virginia, said he thought Mueller had one duty, which was to investigate and report his findings to his boss, Barr. Congress can chose to act as they wish based on the evidence uncovered by the special counsel. Mueller "laid out a thorough and compelling case for obstruction of justice," Rosenberg said. "If it was anyone else on the planet, you'd have a defendant facing charges in federal court."

Rosenberg, a former aide to Mueller, said prosecutors disagree all the time about whether conduct is criminal and whether it can be proven in court.

“Barr is free to disagree,” he said. “I just hope he disagreed for meritorious reasons and not simply to protect an individual.”

The 448-page report provides an inside-the-room narrative of two years of a presidency consumed by congressional and federal investigations into possible ties between Trump’s campaign and Russian officials who sought to influence the 2016 presidential campaign in Trump’s favor. Mueller concluded there was no criminal conspiracy between Moscow and the campaign.

Trump was often deeply angered over the scrutiny the investigation brought and the report shows he acted at times like a bully — screaming at White House Counsel Donald McGahn to fire Mueller in June and pressuring Attorney General Jeff Sessions to help take control of a probe he had decided he was ethically barred from overseeing.

Mueller’s team also reviewed the pattern of Trump’s behavior — stressing the connection between events — to bolster evidence of Trump’s intent to interfere in the probe.

The report described how in June 2017, Trump ordered McGahn, the top White House lawyer, to remove the special counsel for alleged conflicts of interest involving a dispute over fees at one of the president’s golf courses — at the same time he told trusted adviser Corey Lewandowski to convince Sessions to try to limit the scope of the investigation.

“It is important to view the President’s pattern of conduct as a whole,” the report stated. “That pattern sheds light on the nature of the President’s acts and the inferences that can be drawn about his intent.”

One key limitation, allies of the special counsel’s team said, was Mueller’s conservative, button-down approach, in which he tried to follow the letter of the regulations, believing he could not even offer his judgment about Trump’s criminal culpability. Mueller also didn’t explicitly say he was leaving his decision to Congress in his report, leaving questions around his intent even if many consider the body empowered under the Constitution to handle presidential misconduct. And he chose awkward, indirect language to try to explain he didn’t consider the president necessarily innocent of a crime.

“If we had confidence after a thorough investigation of the facts that the President clearly did not commit obstruction of justice, we would so state,” the report stated in its final paragraph. “Based on the facts and the applicable legal standards, we are unable to reach that judgment.”

In comparison, Barr was clear and decisive in his March 24 summary of Mueller’s report.

The “report identifies no actions that, in our judgment, constitute obstructive conduct, had a nexus to a pending or contemplated proceeding, and were done with corrupt intent.”

White House lawyer Emmet Flood criticized the obstruction part of Mueller’s report on a call with surrogates Thursday afternoon, according to people on the call who spoke on the condition of anonymity to discuss a private call. The purpose of the discussion was to get people to attack the investigation in the news media and defend Trump.

Flood called it a “political document” and said he took issue with Mueller releasing such a long report, according to the people on the call. At one point, Silk from Diamond and Silk, a pair of social media personalities who often defend Trump on TV, asked Flood a question and suggested Hillary Clinton, Trump’s rival in the 2016 presidential race, and other officials should be charged with a crime. Flood dodged the question, according to the people on the call.

Throughout the report, investigators detail how they sought to determine why Trump behaved the way he did, if he took an official act, what his intent was and whether his behavior had any impact on the investigation or the actions of people involved.

For example, they conclude the president repeatedly made misleading public comments about a meeting at Trump Tower in the summer of 2016 between top campaign advisers, including his son Donald Trump Jr. and a lawyer with ties to the Russian government. He told aides to provide false or incomplete information to the media and to hold information tightly inside the White House. But Mueller’s team concluded Trump did not commit obstruction because he did not instruct anyone to mislead investigators.

In some instances, investigators found it was difficult to determine Trump’s motivation — the president declined to sit for an interview with Mueller’s team, which found his written responses to a set of questions “inadequate.”

In other cases, they described the president’s intent more clear.

For instance, McGahn refused to accede to Trump’s request to oust the special counsel in June 2017 and to later lie about the conversation when it was reported by the New York Times. Investigators broadly concluded that Trump behaved the way he did “for the purpose of influencing McGahn’s account in order to deflect or prevent further scrutiny of the president’s conduct toward the investigation.”

Investigators probed why Trump repeatedly attacked Sessions, pressuring him to resign or “unrecuse” himself from the Russia investigation. “A reasonable inference from those statements and the President’s actions is that the President believed that an unrecused Attorney General would play a protective role and could shield the President from the ongoing Russia investigation,” the Mueller investigators wrote.

In several instances, investigators concluded it was his aides’ decision not to follow through on Trump’s requests that made it difficult to determine whether there was obstruction of justice.

For example, Rob Porter, Trump’s former staff secretary, declined to approach a senior Justice Department official, Rachel Brand, and ask her to take over the Mueller investigation, as Trump wanted.

Porter was “uncomfortable with the task,” the report says. Trump continued to ask about it, Porter told investigators. “In asking him to reach out to Brand, Porter understood the President to want to find someone to end the Russia investigation or fire the Special Counsel, although the President never said so explicitly.”

Mueller’s investigators also grappled with whether Trump’s directions to then-FBI Director James B. Comey to take it easy on former national security adviser Michael Flynn, who later pleaded guilty to lying to the FBI, during a February 2017 dinner constituted obstruction.

“The circumstances of the conversation show that the President was asking Comey to close the FBI’s investigation into Flynn,” Mueller’s prosecutors wrote. “When he says that he ‘hopes’ a subordinate will do something, it is reasonable to expect that the subordinate will do what the president wants.”

Trump had already been told by McGahn that Flynn’s statements to senior White House officials and the FBI concerning conversations he had about sanctions with Sergey Kislyak, Russia’s ambassador to the United States were not true, the report says.

“Some evidence,” according to Mueller’s report, suggests that the president knew about Flynn’s calls to Kislyak during the transition when they occurred, but “the evidence is inconclusive and could not be relied upon to establish the president’s knowledge.”