It doesn’t seem to matter who sits in the US attorney’s office when it comes to prosecuting union members or the politicians who advocate for them. Democratic appointee Carmen Ortiz prosecuted Joseph Burhoe and John Perry of Teamsters Local 82 for extorting nonunion employers to hire union workers at various fund-raising events. She also prosecuted four Teamsters in connection with the 2014 filming of the reality TV show “Top Chef.’’ While Ortiz began the prosecution of Walsh administration officials Kenneth Brissette and Timothy Sullivan for Hobbs Act violations in connection with their efforts to get union jobs at the Boston Calling music festival, the case against them was enthusiastically finished by Republican appointee Andrew Lelling.

The government’s record isn’t very good — the four Teamsters were acquitted, and the convictions of Burhoe and Perry were reversed, in part because of the ambiguity of the Hobbs Act. The Hobbs Act is a 1946 statute that criminalizes obtaining property from another through “wrongful use of actual or threatened force, violence, or fear.’’ The classic case of “wrongful use of fear’’ is a store owner making protection payments to gang members out of fear that they will trash the store.

Prosecutors try to stretch the law beyond that classic case, prompting warnings from the First Circuit Court of Appeals in Boston, among others. Such prosecutions risk “chilling the ability of conscientious public officials to act on behalf of their political supporters,’’ the First Court said. But while the courts have recognized the danger, other observers, including the Globe editorial board, which applauded the Boston Calling verdict, have not.

Here’s the problem: First, picketing is lawful under the National Labor Relations Act, even if it means “economic calamity’’ for a company, as Lelling described it. That was why the Burhoe and Perry convictions under the Hobbs Act were thrown out; they were merely threatening a nonunion shop with picketing, among other things, to get them to hire union workers — not Hobbs Act extortion.

Second, if a union can threaten a company that doesn’t hire union labor with a strike, why is it extortion when city officials convey the same message — that there will be a picket line, even an inflatable rat, at Boston Calling, if the concert organizers don’t hire union workers?

Third, according to the First Circuit, the legal issue is not the threat of economic harm from the picketing; that comes with the territory. It is whether that threat is designed to achieve a wrongful purpose. What is the wrongful purpose here, according to the government? Rewarding a particular constituency, a union, that had supported the mayor.

One only has to read a few Supreme Court cases to understand the problem. When the Supreme Court three years ago dismissed the case against Governor Robert McDonnell of Virginia, who had accepted money from a wealthy constituent in exchange for introductions to state officials and invitations to formal dinners, the court said: “The basic compact underlying representative government assumes that public officials will hear from their constituents and act appropriately on their concerns,’’ including those who make campaign contributions. In fact, the court cited the example of a union worker who was worried about a plant closing and approached a government official. Labeling this extortion, the court said, it “could cast a pall of potential prosecution over these relationships if the union had given a campaign contribution in the past’’ — just the points that the City Council members made in their recent press conference over the Boston Calling verdict.

Of course, the calculus is different if “advocating’’ involved actual interference with the permitting process. Whatever the initial charges, there was no evidence that that’s what Brissette and Sullivan did. The permitting authorities testified that they made their own decisions, and never heard from the defendants. Even Crash Line, the company supposedly being extorted, agreed; permits were not mentioned by the officials. If the purpose here was to “secure real work for members of a specific union’’ (the First Circuit’s words in an earlier Brissette-Sullivan appeal), how can that be unlawful?

Assume no union involvement: Let’s say a company using city property for a concert doesn’t hire women or minorities. A city official says to the company representative, “If you don’t hire women or minorities, you will be picketed by women’s groups or by the NAACP.’’ And let’s say the support of those groups happened to have been crucial to his boss’s election. Is that extortion or just representative government?

The law doesn’t distinguish between constituents — the ones you are allowed to help, and the one you can’t. In fact, unions are an important constituency. That’s why so many observers are decrying the jury’s verdict.

Nancy Gertner, a retired federal judge, is a professor at Harvard Law School.