The investigation’s techniques are also instructive. The Southern District of New York, to which Mr. Mueller referred the Cohen case, raided the offices of Mr. Cohen, President Trump’s former attorney, and fought for access to the materials, even as Mr. Cohen asserted attorney-client privilege. When federal prosecutors investigate large companies, out of custom and deference they rarely use such aggressive tactics. They place few wiretaps, conduct almost no undercover operations and do almost no raids. Instead government attorneys reach carefully negotiated agreements about which documents they can review, the product of many hours of discussion with high-powered law firms on behalf of their clients. All the battles over privileged materials happen behind closed doors and without the benefit of a disinterested special master, as the Cohen case had.

Indeed it’s worse than that. The government has essentially privatized corporate law enforcement. The government effectively outsources the investigations to the companies themselves. The companies, typically trying to appear cooperative or to forestall government action, hire law firms to do internal investigations. Imagine if Mr. Mueller relied on Mr. Trump to investigate whether he colluded with the Russians or violated any other laws, and Mr. Trump hired Rudy Giuliani’s firm to do the inquiry.

The aggressive Mueller techniques have yielded the most crucial element for white-collar cases: flippers — wrongdoers who agree to testify against their co-conspirators. Rick Gates, the Manafort protégé, helped tighten his mentor’s noose. We are going to see in the next few months how many people flip and what they will say. No wonder President Trump mused that flipping “almost ought to be illegal.”

Mr. Mueller’s experience has given him the courage to take cases to trial, where juries are mercurial and the federal bench has turned hostile. Mr. Mueller’s prosecutors tried a “thin case” against Mr. Manafort, as the expression goes, boiling their evidence down to a few elements that the jury could easily absorb. They even managed to overcome the open hostility of U.S. District Court Judge T.S. Ellis. Good prosecutors are used to that in white-collar cases. Judges and justices have not looked favorably upon white-collar prosecutions for more than a decade now, overturning verdicts and narrowing statutes. But with well-marshaled evidence and clear presentation, prosecutors can surmount the difficulties.

Moreover, Mr. Mueller isn’t looking to go soft to preserve his professional viability. I’m assuming that at age 74, he’s not going to go through the revolving door after this. That hasn’t been true for most top Justice Department officials in recent years. Many of them start out defending large corporations, and when they leave government they go back to the same work of defending large corporations.

The same goes for the younger prosecutors who negotiate those corporate settlements. Almost all go on to become corporate defense attorneys. In those negotiations, they are auditioning for their next jobs, wanting to display their dazzling smarts but also eventually needing to appear like reasonable people and avoid being depicted by the white-collar bar as cowboys unworthy of a prestigious partnership.