“I believe in America.”

So says Amerigo Bonasera, a humble funeral director, in the opening scene of the 1972 film The Godfather. As Barbara McQuade recounts at the start of her new book, Bonasera has come to the shadowy office of Vito Corleone to ask him to avenge a brutal attack on his daughter. Ultimately, Corleone agrees, whispering: “Someday, and that day may never come, I’ll call upon you to do a service for me.”

The lesson that McQuade, a former federal prosecutor, draws from this is that Corleone is demanding fealty. “What he’s saying is I’m going to do this thing for you but now you’re beholden to me.” And for Don Corleone, she says, read Donald Trump. “Every time he does somebody a favour, whether it’s an appointment or something else, he expects there to be a quid pro quo.”

It is a principle that informs The Fix: Saving America from the Corruption of a Mob-Style Government, a piercing exposé of how the president is eroding democracy by turning the US into a mafia state – with some proposals for how ordinary citizens can fight back. There is even a cover blurb from the Godfather Part II star Robert De Niro.

McQuade, 61, is a professor at the University of Michigan Law School and legal analyst for the MS Now network. From 2010 to 2017 she served as the US attorney for the eastern district of Michigan. She has prosecuted high-profile corruption cases, including that of the former Detroit mayor Kwame Kilpatrick, as well as the “underwear bomber” Umar Farouk Abdulmutallab and the Volkswagen emissions scandal.

Now she turns her prosecutorial gaze on the occupant of the White House and makes the case that Trump governs like a mob boss. “He uses his power to try to control others, especially would-be critics,” she says, sitting outside Comet Ping Pong, a Washington pizza joint targeted in 2016 by an armed man motivated by the baseless conspiracy theory that it was harbouring children as part of a Democratic-led child sex-trafficking ring.