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From the moment he was appointed special counsel, he knew that he was walking on eggshells, that a "Saturday Night Massacre" (like Nixon’s firing the special prosecutor Archibald Cox) could be just around the corner. And as he dug deeper into the case, his concerns had to have grown exponentially — Trump’s reaction to the appointment of a special prosecutor (that it was “the end of his presidency”), demanding Attorney General Jeff Sessions’ resignation, directing White House counsel Don McGahn to fire Mueller, and then to lie about it, falsely claiming that Mueller had conflicts of interest and must be removed.

At any moment, Mueller had to believe the hammer would fall.

And that pressure plainly impacted what Mueller did and how he did it. He was going to stay in his lane — no matter what. He was going to produce a report even more scrupulous than it had to be. He would not consider new criminal theories — like the crime of accepting a “thing of value” from a foreign government during an election. He would not consider any claims that grew out of his investigation, like the claim that Trump conspired to commit election fraud when he paid off women who alleged he had affairs with them, even though Mueller surely could have. He wouldn’t press the president to testify in person, even though, as special counsel, he had the right to issue a subpoena. And he would conclude this investigation as expeditiously as possible, careful not to release it near an election.

While he listed in detail at least 10 instances in which Trump attempted to obstruct justice, he would not pull the trigger; he would not draw the conclusion that seems obvious from the report. He wouldn’t take that step, even though hundreds of former federal prosecutors did so in a May 6 letter.

Mueller claimed that he didn’t conclude guilt because the Justice Department Office of Legal Counsel's (OLC) guidelines say that a sitting president can’t be indicted, but that explanation doesn’t fly. Just because a sitting president can’t be indicted doesn’t mean a special counsel is barred from determining whether a crime was committed at all. In fact, the OLC policy suggests just the opposite: It rejects indicting a president because the impeachment remedy is supposed to have priority over the ordinary criminal processes. And Mueller’s report, as well as his conclusions, are as important for that impeachment inquiry as it would be for an indictment.

Nor does it make sense that he refrained from concluding the president was guilty because of DOJ’s practice to refrain from public comment on evidence in cases where charges are not brought. The rationale for the practice is to avoid public discussion of evidence that falls short of being enough to charge a person with a crime. That’s why in the Clinton email investigation, the inspector general found no basis for “trashing" the subject of an investigation with uncharged misconduct that FBI Director James Comey, every agent and every prosecutor agreed did not warrant prosecution (emphasis added). But the rationale against public comment does not apply where Mueller does find sufficient evidence of criminal conduct but doesn’t charge him, just because of the OLC policy.

No, Mueller didn’t draw any conclusion about whether the president obstructed justice — nor would he exonerate the president — because he was cautious, he didn’t want to say one word more than he had to. He wanted to stay in his lane, to avoid partisan attacks, preserve the integrity of his investigation.

He badly miscalculated. He stayed in his lane, but no one else did. Attorney General William Barr spun Mueller's conclusions, disparaging him and his work. President Trump took the cue and claimed "no collusion, no obstruction" when that's not what the report says. Conservative media followed suit. Mueller wholly misjudged the political climate in which his careful, lawyerly report would be received.

So I wasn’t entirely surprised by his testimony. “Entirely,” though, is the key word here. He wouldn’t even read the words of his own report. He wouldn’t get indignant even when the bona fides of his staff of prosecutors were attacked. The moment he even came close was when he expressed concern about the president’s overtures to WikiLeaks. The only indignation in the room came from his questioners, the representatives — and that just collapsed into the traditional partisan patois.

This performance was not the performance of the man I know, a zealous advocate against whom I squared off against 30 years ago in several criminal cases. Nor was it the performance of the former FBI head who skillfully, even aggressively, parried the pointed questioning of Congress and the media. His performance this week was so passive, so restricted, so crabbed that many speculated he was impaired in some way.  And for a man with his extraordinary career, who took the special counsel job to cap off his life of service, that is even more troubling.