Bill Hennessy / Reuters

For months, Special Counsel Robert Mueller has pushed inexorably forward, delivering indictment after indictment and guilty plea after guilty plea. The track record, combined with Mueller’s public silence outside of court filings, have given his probe the appearance of a grim juggernaut, and inspired sky-high hopes among Donald Trump’s detractors—along with thriving markets in meme T-shirts and devotional candles improbably dedicated to the former FBI chief.

On Thursday, the juggernaut landed in a ditch.

In a hearing in Alexandria, Virginia, Judge T. S. Ellis III sentenced Paul Manafort, President Donald Trump’s 2016 campaign chairman, to 47 months in prison on bank fraud and tax-evasion charges. That falls well below the 19 to 24 years recommended by the sentencing guidelines, and while Mueller’s team didn’t ask for a specific sentence, they pressed Ellis to throw the book at Manafort. The judge declined, and his decision represents the most prominent defeat that Mueller has suffered so far.

There are caveats: Yes, Ellis had already tangled with prosecutors during Manafort’s trial. Yes, Mueller will get another chance with Manafort in a separate sentencing hearing next week in the District of Columbia. Yes, it’s still a huge deal that the president’s former campaign head committed multiple felonies and will serve nearly four years in jail. But it’s also impossible to view this as anything other than a setback for Mueller.

President Trump certainly sees it that way, celebrating the ruling in a morning tweet that was, by his recent dour standards, positively ebullient:

The sentence is a surprise. Defense attorneys were quick to post examples on social media of harsher sentences given to those convicted of lesser crimes. In the course of acquiring eight felony convictions, Mueller’s team had presented documentary evidence of Manafort’s years of cheating the system. They also came close to convicting Manafort on another 10 charges, but a lone holdout on the jury blocked guilty verdicts.

The short prison term would have been an even bigger surprise had Ellis not expressed deep skepticism of the government’s case during the trial. At one point, he even walked back barbed comments directed at Mueller’s prosecutors, acknowledging that he had overstepped. And as my colleague Franklin Foer writes, Ellis’s statement that Manafort had “lived an otherwise blameless life” is impossible to square with the public record.

There are other important caveats. Because Manafort opted for separate trials in Virginia and Washington, D.C., he will be separately sentenced in Washington next week, and Judge Amy Berman Jackson has seemed less favorably disposed toward him thus far. That case deals with different offenses, too: Manafort pleaded guilty to witness tampering and conspiracy related to his lobbying work in Ukraine. Since saying in December that Manafort reneged on a plea deal by lying, a conclusion Jackson backed, prosecutors have presented evidence of additional crimes. Jackson could yet impose a steep sentence.

Contrary to what Trump said in his tweet, Ellis said on Thursday that Manafort “is not before the court for anything having to do with colluding with the Russian government.” Yet this is less exculpatory than it initially appears, since the Washington case goes much closer to the heart of the collusion question than the financial crimes in the Virginia case.

Moreover, it’s still a major development for Manafort to go to prison. When Trump hired Manafort, he had ample warning about the miasma of scandal that surrounded him and did it anyway. Mueller has so far shown that Trump surrounded himself with criminals—Manafort, the former National Security Adviser Michael Flynn, the former fixer Michael Cohen. Even now, as yet incomplete, it is one of the worst scandals in American presidential history.

But this is the way the law works: It’s unpredictable and erratic, subject to the whims of a single juror, as in the holdout, or a single judge, as in Thursday’s sentence. Historically, setbacks have been the rule for special counsels. Iran-Contra’s Lawrence Walsh was stymied by Congress and by pardons; Ken Starr found nothing on Whitewater, and suffered some defeats in court as he pursued other matters. This is how it should be. A system in which a prosecutor gets anything he wants is unlikely to deal real justice.

The cult of Mueller veneration is predicated on an image of the law as unflinching and mathematical. Yet the special counsel is not judge, jury, and executioner—he is just a prosecutor. That’s a good thing, the bedrock of the legal system. It also shows why, contrary to Trump’s protestations, the president is not being railroaded by the system. In a saner world, Manafort’s light sentence would temper Trump’s cries of “witch hunt.” In the real world, Mueller is not invincible, and the president continues to tweet.

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