There was something about then-Rep. Duke Cunningham’s explanation of a pair of overseas Congressional trips that brought out the skeptic in Marcus Stern.

In 2005, the California Republican told Stern, a reporter for Copley News Service, that he went on two trips to Saudi Arabia to “promote discourse and better relations” between the U.S. and the Saudis.

Stern’s suspicion about that statement led to reporting by him and a Pulitzer Prize-winning team of journalists and an investigation that eventually landed Cunningham an eight-year, four-month sentence in federal prison.

The group’s new book, “The Wrong Stuff,” which is on bookshelves Monday, chronicles Cunningham’s ride from patriotic pilot to corrupt Congressman.

So why would two simple Congressional trips be a red flag? After all, hundreds of such trips occur each year. The answer lies in the reputation Cunningham had developed in Congress, according to Stern.

“Cunningham is just not the type of guy who goes on a trip to improve relations,” the reporter said in an interview. “I’ve been to Saudi Arabia, and I didn’t find it a comfortable place to be as a reporter or a Westerner or an outsider. I could see Cunningham going there once, by mistake, but I definitely didn’t see it as his kind of place and couldn’t see him going back.”

Although Stern never found anything inappropriate about the trips, they did get him poking around for details of Cunningham’s life.

A database search finally revealed the purchase of a mansion in the wealthy San Diego suburb of Rancho Santa Fe, an area Stern thought Cunningham couldn’t afford. That purchase, it turned out, was made possible by the inflated price at which Cunningham sold his previous house to defense contractor Mitchell Wade.

An article about the home sales ran in the San Diego Union-Tribune on June 12, 2005, and the FBI immediately opened an investigation that would discover millions more in bribes. [IMGCAP(1)]

The book traces Cunningham’s demise to May 10, 1972, when as a fighter pilot in Vietnam he shot down three enemy planes, giving him a career total of five kills and making him an “ace,” to use the term coined in World War I. That is the day, Stern and Co. write, that Cunningham “actually became the Duke and fully took on the persona that was to carry him to stardom, wealth, fame, political power, and — ultimately — shame, dishonor, and prison.”

The authors describe Cunningham being taken over by a sense of entitlement — to the point that he tried to decline a Navy Cross, the Navy’s top award, in hopes of getting the more prestigious Medal of Honor.

The officer in charge of the award ceremony, Ron McKeown, responded that “the way you get the Medal of Honor is you don’t hold out for it — you die for it,” according to the book, and he ordered Cunningham to accept the Navy Cross or “I will personally rip your tits off.”

“The essence of his life was the day he shot down those three MiGs,” McKeown says in the book. “After that everything else was sort of frozen in time. You could talk about anything, from quantum physics to football, and he would somehow twist it around to … that day.”

An F. Scott Fitzgerald line, “Show me a hero and I’ll write you a tragedy,” is the epigraph to “The Wrong Stuff.”

“That really summed up what this was about on a personal level,” Stern said. “Those seven minutes in the skies over Vietnam were the culmination of a lot of training and certainly showed a lot of courage and skill on his part, but he didn’t handle that status as a hero very well. And maybe that’s because he wasn’t a hero with a capital H, wasn’t a heroic human being in terms of his character.”

Beyond just telling the story of Cunningham’s downfall, the authors — Stern was joined in the book by Copley’s George E. Condon Jr. and Jerry Kammer and the San Diego Union-Tribune’s Dean Calbreath — use it as a case study in openings for corruption in the earmark process and convey their desire for reform.

“This was not a news article; this was a book. We said in a book we had to have a voice and draw conclusions,” Stern said. “We purposefully and consciously took on a voice and finished with something more akin to a call to action than anything we’d do in a news story.”

Stern said he is proud of his and his colleagues’ work.

“I’d like to think that somebody else would have eventually noticed Cunningham was living in a mansion in Rancho Santa Fe stuffed with antiques, but I don’t know when that would have happened,” he said.

“It is satisfying as a journalist to make a difference. We spend a lot of time kicking under stones and there’s nothing under there. This was a case where there really was something there, and there was a whole lot more corruption than I ever imagined.”