WASHINGTON — Special Counsel Robert Mueller’s decision that he could not conclude whether President Trump’s attacks on the Russia investigation amounted to obstruction of justice illustrates the difficulty in proving such a charge — and left Democrats with a narrow and fraught path to press a case against Trump.
In the end, Trump’s mercurial behavior and relentless attacks on the FBI and special counsel probably extended the length of the probe — but the fact that many of his eruptions were in public view also may have made it more difficult to show that he had ill intent, a key element in proving obstruction, legal experts said.
In his still-confidential report, Mueller stopped short of drawing a conclusion about whether the president obstructed justice, writing that ‘‘while this report does not conclude that the President committed a crime, it also does not exonerate him,’’ according to a summary by Attorney General William Barr, released Sunday.
Barr went further, saying he and Deputy Attorney General Rod Rosenstein concluded that the evidence gathered by the special counsel ‘‘is not sufficient to establish that the President committed an obstruction-of-justice offense.’’
That has left the question of Trump’s actions — which included the firing of FBI Director James Comey, the public attacks on then-Attorney General Jeff Sessions, the regular cries of ‘‘witch hunt,’’ and the taunting of witnesses — as one that will now be wrestled with in the political arena.
The obstruction question, as a legal matter, came down to whether the special counsel had evidence that Trump acted with ‘‘corrupt intent’’ as he demeaned and demonized the investigation.
‘‘Proving intent is genuinely difficult, because it requires you to get inside someone’s mind — and divining intent is art, not science,’’ said Chuck Rosenberg, a former US attorney in Virginia and former counsel to Mueller.
Rosenberg said he was not surprised by the special counsel’s difficulties in drawing a conclusion on obstruction, noting that it is a complicated calculus to prove someone intended to block investigators and hide a crime.
‘‘It was something we routinely debated, as prosecutors and agents,’’ he said.
In his report, Mueller addressed obstruction in an unusual way: He laid out evidence on both sides of the question but left ‘‘unresolved what the Special Counsel views as ‘difficult issues’ of law and fact,’’ Barr wrote in his summary. And Mueller pointedly did not clear the president.
One major factor in the Justice Department’s analysis: Since Mueller concluded that the Trump campaign did not conspire with Russia as it interfered in the 2016 campaign, prosecutors could not argue that he acted corruptly to hide an underlying crime, legal experts said.
Prosecutors can seek a charge of obstruction when someone seeks to thwart a known criminal investigation, even if there wasn’t an underlying crime, some legal experts said, but they said it can often be difficult to then prove that case to a jury.
Compounding the challenge for Mueller was Trump’s refusal to sit for an interview in which prosecutors could have probed his motivations.
Instead, his legal team only provided written answers from the president to Mueller’s questions about the campaign — not Trump’s activities in the White House.
And some of Trump’s actions — such as his firing of Comey — represented the exercise of powers afforded to the president by the Constitution, as his lawyers often argued.
To find criminal obstruction, a prosecutor must have evidence that a person’s actions would have the ‘‘natural and probable effect’’ of disrupting an investigation, said Mary McCord, former acting head of the Justice Department’s National Security Division, who oversaw the early stages of the investigation.
Barr wrote in his Sunday memo to lawmakers that Trump’s actions — many undertaken not furtively, but in full public view — didn’t reach that standard.
David Kris, who ran the national security division of the Justice Department in the Obama administration, said it was ‘‘notable’’ that Barr and Rosenstein came to a conclusion about the president’s actions within 48 hours of receiving Mueller’s final report, which was submitted late Friday.
‘‘Attorney General Barr, in the space of a weekend, is able to make the judgment that Mueller precisely avoided making and described as being ‘difficult,’ ‘‘ said Kris, who now runs the consulting firm Culper Partners.
‘‘On the merits, then, Barr and Rosenstein together have reached the question that Mueller specifically avoided reaching, and they reached it very rapidly,’’ he said.
The attorney general’s assessment came after months in which Trump repeatedly sought to discredit the Russia probe, making public attacks that bewildered his staff.
Trump advisers often joked that the president’s actions made them think he was guilty, even as he said he was not. ‘‘Why would you behave that way if you’d done nothing wrong?’’ said one former senior administration official, who, like others, spoke on the condition of anonymity to describe internal discussions.
But Trump’s legal team long argued that Trump had no corrupt intent and that he was not intending to block the FBI inquiry into Russian activity, which began before he took office and was taken over by Mueller in May 2017.
Chris Christie, the Republican former governor of New Jersey, said he warned the president repeatedly that his actions could only prolong the probe.
‘‘He is always on offense. He never ever stops. Sometimes it works to his benefit, sometimes it works to his detriment,’’ Christie said Sunday.
Trump’s actions provided a rich area of inquiry for the special counsel and his team. Comey has said that Trump told him in an Oval Office meeting in February 2017 that he hoped Comey would let go of an investigation into whether Michael Flynn, who was then national security adviser, had lied about his contacts with the Russian ambassador. (Trump later denied that he made the request.)
When Trump fired Comey, he told a Russian diplomat in the Oval Office and then an NBC News reporter that he did so with the Russia investigation in mind.
He then spent months on Twitter badgering Mueller and Sessions, the attorney general who had earned Trump’s ire by recusing himself from the probe — and who was eventually forced out in November. He told aides at one point that he wanted to fire Mueller.
In Congress, Democrats promised they would pick up where Mueller left off, insisting that they must see the special counsel’s full report.
But for Democrats, there could be political risk in pressing the question.
‘‘The American people will long remember how wrong and irresponsible the Democrats have been,’’ House GOP Conference chairwoman Liz Cheney of Wyoming said in a statement Sunday.