The news that Rudolph Giuliani is under investigation by federal prosecutors in Manhattan hasn’t gained quite the attention it should. The New York Times put the story on its front page earlier this month under a four-person byline, attributed to two anonymous “people familiar with the inquiry.”

The Times characterized it as “a stark turn for Mr. Giuliani, who now finds himself under scrutiny from the same United States attorney’s office he led in the 1980s, when he first rose to prominence as a tough-on-crime prosecutor.”

A “stark turn” is indeed one way of looking at it, describing the potential change in Mr. Giuliani’s role from prosecutor to prosecuted. No charges have been filed against the former mayor of New York, and Mr. Giuliani has denied any wrongdoing. Four Giuliani associates—David Correia, Lev Parnas, Igor Fruman, and Andrey Kukushkin— were arrested this month on campaign-finance-related charges.

What’s striking is that the tactics faced by Mr. Giuliani and his associates — and others in recent years — almost precisely echo those that Mr. Giuliani himself used in the late 1980s against financial industry figures such as Michael Milken, Richard Wigton, or Timothy Tabor. There’s the use of criminal charges to handle issues that are more appropriately considered civil violations, if they are violations at all.

There’s the use of anonymous leaks to the press to cast a cloud of suspicion and make it harder for someone to get a fair trial. There’s the “crimes” in which victims are scarce and so is the constitutional basis for the crime. There are incentives created for individuals to strike deals with prosecutors by “flipping” and implicating others in exchange for promises of leniency.

There’s the use of criminal law to pursue political goals. There are charges announced with great fanfare only to be reduced or reversed later in the judicial process.

Prosecutors attempting overreach in recent cases have been emphatically rebuffed by federal judges. President Obama’s White House Counsel, Greg Craig, was acquitted by a federal jury earlier this year on one count after a judge threw out the other count. This was a case in which Mr. Craig’s “crime” was related to talking to his neighbor, New York Times reporter David Sanger, about work that Mr. Craig and his then-law-firm did for the Ukrainian government.

In a second Foreign Agents Registration Act-related case this year, a federal judge in Virginia issued a ruling acquitting Bijan Rafiekian of having acted as an unregistered foreign agent of Turkey.

If federal prosecutors try going after Giuliani on Foreign Agents Registration Act-related charges, Mr. Giuliani is likely to win, just as Messrs. Craig and Rafiekian did. Same on charges of unregistered lobbying. The notion that lobbyists need to register is itself an offense against the First Amendment-protected freedoms of speech, petition, and assembly.

As for the campaign finance charges, we’ll see what, if anything, prosecutors have to say. There, too, freedom of speech is an issue. And just as Wall Street violations are often more appropriately handled with civil fines and penalties imposed by the Securities and Exchange Commission than by the criminal justice system and prosecutors, election law violations are often better handled with civil penalties or fines imposed by the Federal Election Commission.

The irony is that if Mr. Giuliani has defenders in a coming legal battle, they’ll be the principled civil libertarians and critics of prosecutorial excess who were his fiercest critics in the late 1980s. The legal environment is currently poisoned by a strange confluence of xenophobia and anti-Trump sentiment, with the ones most bitterly critical of Mr. Trump’s supposed xenophobia also somehow supremely confident that he and his aides are tools of Russia, Ukraine, Turkey, or Saudi Arabia, or even, in the case of his transportation secretary Elaine Chao’s family, it is recklessly alleged, China.

In the late 1980s, jealousy of Wall Street financial success spilled over into the legal system. Today it is jealousy of the political success of Mr. Trump and his circle. I hope Mr. Giuliani escapes legal persecution of the sort that Mr. Giuliani himself once wreaked on Michael Milken. But if it does come to that, perhaps Mr. Giuliani can console himself with the knowledge that people eventually, as in Milken’s case, do come to see these prosecutions for what they are.