For example, Mr. Barr quoted a fragment of one of Mr. Mueller’s sentences about how the evidence did not prove there had been any agreement between the campaign and Russia, but omitted a lead-in about how the Trump campaign had many contacts with Russians and had welcomed Russian intervention.

And while Mr. Mueller’s investigators wrote about several actions by Mr. Trump that seemed to meet the criteria for obstruction, while stopping short of deciding whether to accuse Mr. Trump of that crime because the Justice Department has said sitting presidents cannot be indicted, Mr. Barr explained none of that. He simply declared that Mr. Mueller had made no call, leaving it to the attorney general to decide that the evidence did not support obstruction charges.

Still, in other ways Mr. Barr’s performance has not lived up to critics’ fears about him. During his confirmation hearing, Democrats expressed worries that he would invoke his broad view of executive power to tell Mr. Trump that the Constitution puts him, as president, above the law. Mr. Barr has written that obstruction laws cannot cover a president who abuses his official powers to impede an investigation, and argued for a sweeping view of a president’s authority as commander in chief.

Against that backdrop, it was notable on Wednesday that he invoked no constitutional theories to justify clearing Mr. Trump of obstructing justice. Rather, he interpreted the evidence in a light favorable to Mr. Trump, arguing that it was ambiguous and fell short of proof beyond a reasonable doubt that any of his actions met the criteria for obstruction.

But Mr. Barr at times seemed to channel the vantage point of a defense lawyer for Mr. Trump that was at odds with the image of an attorney general who enforces the law dispassionately. Senator Amy Klobuchar, Democrat of Minnesota and a former prosecutor, pressed him to explain how it was not obstruction of justice for Mr. Trump to dangle a pardon before his former campaign chairman, Paul Manafort, while urging him not to “flip” and cooperate with investigators.