Ex-federal prosecutor points out the biggest question Barr will have to answer when he finally releases the Mueller report

On Friday, former federal prosecutor Renato Mariotti wrote an editorial outlining the most important aspects of special counsel Robert Mueller's investigation of Russia, and its findings on President Donald Trump, that the public needs to know.

"My attention will immediately focus on one specific aspect of the report:Mueller's explanation of why he declined to 'make a traditional prosecutorial judgment' regarding obstruction of justice," wrote Mariotti. "This is the part of the report that could have the most immediate public consequences, since it bears most directlyon the offense that could cause Democrats to seriously push for impeachment."

For one thing, Mariotti noted, the answer could show he simply wanted to leave it up to Congress, in which case Attorney General William Barr's decision to reach his own conclusions in a public summary looks even worse.

"Barr's legacy will be forever defined by that decision if the report indicates, contrary to what Barr suggested, that Mueller intended to leave the obstruction decision to Congress or the American people," wrote Mariotti. "In that scenario, congressional Democrats are sure to distrust Barr's redactions, will push even harder to see the full report and could take a harder look at obstruction of justice."

While Trump's actions around the investigation look very suspicious, like firing FBI Director James Comey, Mariotti cautioned that there could in fact be complicating factors in Mueller's decision not to make a determination of obstruction. For example, Mueller could have found it difficult to prove Trump's state of mind, or he might never have been warned by former White House Counsel Don McGahn that dismissing Comey could raise obstruction issues.

"If the redacted report reveals disturbing new details regarding obstruction of justice, or indicates that Mueller did not intend to leave the decision in Barr's hands, Nadler and other Democrats could feel more comfortable suggesting that they need to consider impeachment," Mariotti concluded. "Barr's credibility would take a hit, something a court would consider if he does not back off his bizarre refusal to produce the full report to Congress."