Now that Robert Mueller has closed up shop as special counsel and shot off fireworks at his final press conference, the country can step back and assess the job he did. The results are decidedly mixed.

Mueller made two vital contributions. The first was an in-depth investigation of Russian interference in the 2016 election. He concluded it was systematic and favored Donald Trump. The second was an intensive examination of possible coordination between the Russians and the Trump campaign. He concluded that no charges were warranted against any Americans.

The country needed those investigations and Mueller deserves praise for conducting them. More ambiguous was his non-finding of obstruction against the president, which, predictably, has been subject to deep partisan divisions.

Mueller’s two-volume report leaves several big, unanswered questions, though Democrats and Republicans differ on what they are. Democrats, focusing on the second volume, firmly believe Trump interfered with Mueller’s probe. All want further investigations; some want impeachment. Since the Senate is unlikely to convict — the evidence is too thin to win a two-thirds majority — the Democrats’ practical goal is to damage Trump’s chances in 2020. Their political problem, well understood by House Speaker Nancy Pelosi, is that a doomed effort will hurt the Democrats even more.

Republicans reject the obstruction claims, noting that Trump provided millions of documents and gave Mueller unprecedented access to White House staff. Even if Mueller believed he could not indict a sitting president, he could have said the evidence justified it. He made no such statement, though he did list some instances that might be considered obstruction.

Republicans add three more serious charges against Mueller. First, his team was packed with partisan Democrats, many closely affiliated with Hillary Clinton and strongly biased against Trump. Second, the report itself was shoddy and unfair, they say. It relied heavily on news articles, omitted exculpatory evidence, failed to investigate the infamous “Steele dossier,” and never asked why, if Russians were trying to penetrate the Trump campaign, the candidate himself was not told by the FBI. Another serious charge — deliberate distortion of evidence — comes from president’s former attorney, John Dowd. He has shown the Mueller report edited one of his phone calls to change its meaning. Dowd is apoplectic, calling the report a “fraud.” Others will join him if additional distortions, misrepresentations, and omissions are found.

Third, Mueller should have known at least a year ago, and perhaps earlier, that Trump and his senior aides never cooperated with the Russians. He had a duty, Republicans say, to disclose that in a timely way to the American public. He failed in that duty, leaving an unnecessary cloud over Trump and impeding his presidency. Why? And why didn’t Rod Rosenstein, who was supervising the investigation for the Department of Justice, step in and resolve these issues?

Of course, Republicans think the real subversion of justice was committed by the Obama administration’s DoJ, FBI, and intelligence agencies, both in their investigations of Trump and in whitewashing the email case against Hillary Clinton. Attorney General William Barr is already looking into those charges, as are DoJ Inspector General Michael Horowitz and U.S. Attorneys John Durham and John Huber. The chief judge of the secret intelligence courts, Rosemary Collyer, has already delivered a report to DoJ saying that the court was not given full, truthful information in warrant applications.

These investigations could burgeon into a catastrophic scandal, involving not only leaking, lying, and illicit spying but possibly collusion by U.S. government agencies to affect the outcome of an election. We don’t know that yet, and we don’t know the role the Obama White House played, but we need to know.

How do these issues affect Mueller’s reputation? First, his entire investigation was based on two fragile pillars, which Mueller never questioned. If they collapse, Mueller is buried in the rubble. The first pillar is the FBI’s dubious “origin story.” The bureau states, and Mueller explicitly accepts, that its Trump investigation began in late-July 2016 after a low-level campaign volunteer, George Papadopoulos, spoke about Russia to an Australian diplomat in a London bar. Apparently, Papadopoulos also made exculpatory comments, which were not included (as legally required) in a subsequent search-warrant application.

But there is mounting evidence that Papadopoulos was not the first target and July 2016 was not the real starting date. Counter-intelligence investigations of Trump and his associates apparently began earlier and were never disclosed. Neither was widespread illegal spying on Americans by intelligence agencies and their private contractors. Still more surveillance was outsourced to friendly foreign intelligence agencies, which relayed their findings to Washington. Mueller never mentioned these problems — and possible crimes.

These omissions matter. They illustrate bias against Trump and suggest the report’s evidence may be tainted by omission and commission. They show Mueller’s extraordinary efforts to protect the law-enforcement institutions where he served for so many years. That protective shield is a problem because misconduct at DoJ and FBI is central to the inquiry.

The bias issue burst open again after Mueller’s press conference on May 29. Its purported aim was to erect a “Going Out of Business” sign. Since that could have been done with a short, written statement, its real purpose has been debated. Three seem likely. First, he was obviously spinning the report’s conclusions, perhaps to counter what he considered Barr’s spin. Second, he was signaling Congress that, although he could not indict, they could certainly impeach. Finally, he was saying, “I don’t want to testify and, if I must, I won’t say more than the report does.” His invitation to impeach the president infuriated Republicans. His “I won’t say any more” declaration may be meaningless since Congress can subpoena his testimony and demand answers. Trump and Barr have already indicated they will not block it.

Perhaps the worst self-inflicted damage was Mueller’s “not not guilty” statement about Trump. His exact quote: “If we had had confidence that the president clearly did not commit a crime, we would have said so.” That statement is a frontal assault on the oldest, deepest principles of Western law:

No one has to prove their innocence; everyone is presumed innocent until proven guilty, and that includes the president, Supreme Court nominees, and anyone else; and

Prosecutors should never pronounce guilt before a verdict or assert someone committed crimes or “bad acts” without charging them. Either charge a crime or shut up. Mueller missed an excellent opportunity to shut up.

In violating these fundamental legal principles, Mueller mirrored the infamous 2016 press conference by then-FBI Director James Comey, where he detailed Hillary Clinton’s (alleged) misdeeds and then declined to charge her. The charging decision should have been made by the DoJ, not the FBI, and the allegations should never have been mentioned unless they were charged. Comey’s press conference is an act that will live in infamy.

It is stunning to see an experienced prosecutor like Robert Mueller repeat the error. The best explanation comes from a classic comedy sketch by Peter Cooke and Dudley Moore. It ends with Moore asking his friend, “Do you feel you've learnt by your mistakes here?” “Yes,” Cooke replies, “and I think I can repeat them almost perfectly.”

That, sadly, is how Robert Mueller is ending his public service. He learned from James Comey’s mistakes. And he repeated them almost perfectly.