In “The Ambassador: Joseph P. Kennedy at the Court of St. James’s, 1938-1940,” Susan Ronald fashions a portrait of the ambitious Kennedy that brings to mind the mythological figure Icarus. Ignoring a warning to temper his pride, Icarus flew too close to the sun on wings made of feathers and wax that melted, plunging him to his death in the sea. When Kennedy, father of nine, including sons John, Robert and Edward, was named ambassador to Britain, he was instructed to accurately reflect the policies of President Franklin D. Roosevelt. Or at least, not contradict him. That is, behave like a diplomat.

But Kennedy was no diplomat, and he had no interest in imitating one. He was a boorish, stubborn man who got the ambassadorship mostly because he donated to Roosevelt’s 1936 reelection campaign and then demanded the prestigious position in return, as a steppingstone to the presidency. At the next Democratic National Convention, or perhaps the one after, the freshly minted ambassador expected to secure the nomination and sail into the White House. He hoped to launch America’s first Catholic political dynasty with himself as the first Kennedy president. But his pride and bald ambition took him a little too close to the sun.

He already had a spectacular story: He was the grandson of an Irish immigrant who worked so hard he died before he was 40, and the son of a Boston ward boss and barkeep. Kennedy’s shrewd business sense (in the stock market, real estate and even Hollywood) produced a fortune so immense, he encouraged his children to follow their passions (preferably politics for the boys and whatever his daughters wanted, as long as they married by 30). He served as the first chairman of the Securities and Exchange Commission and directed the Federal Maritime Commission. But Kennedy wanted his boss’s job, and FDR knew it.

“The first time he opens his mouth and criticizes me, I will fire him,” the president reassured advisers. Whatever FDR’s threat, Kennedy, who had always been a monomaniacal isolationist, voiced his personal opinions without reservation, while the president was noncommittal in public. He had to be, even as German troops stormed across Europe. The U.S. military was unprepared for war, Americans were reluctant to enter it, and Roosevelt didn’t have permission to declare it. Congress, determined to keep America out of another foreign war, had responded to Adolf Hitler’s rise to power in 1933 by passing three Neutrality Acts. Roosevelt tried to work around these nonintervention efforts, offering England advice and military supplies. The ambassador, meanwhile, spent his days “sticking a knife into the presidential hide,” as Ronald puts it, a practice he extended to the British, too. Stop “resisting Hitler,” Kennedy urged them. He told an adviser to Roosevelt that the British should “let Hitler take over all of Europe.” If it didn’t work out, America could assassinate the Fuhrer, reasoned Kennedy — who all the while was trying to secure a personal meeting with him. Fascism was the future, he believed, and neutrality best for the American economy. Democracy was dead in England and would soon be everywhere else, too. Kennedy made these arguments in opposition to his sponsor and to morality; details about every stage of the Nazi persecution of Jews, from pogrom to concentration camp, flooded his embassy from the day he arrived in London.

At first, England smiled upon the ambassador — a title he would insist on for the rest of his life — and his large family. The London papers praised Rose, his wife, for her youthful good looks and stylish dress. Kennedy’s daughter Kathleen, known as Kick, attracted great attention. Rosemary, who had developmental disabilities, was happy at a Montessori in the countryside, as were the younger children, who settled into their new life. Joe Jr. and John, the eldest sons, were doing original research for their Harvard theses in a rapidly changing Europe.

Eventually, Ambassador Kennedy exhausted the patience of the president. He went too far in his obsession to keep America out of war. On a holiday trip home in 1940, Kennedy, in cahoots with other powerful isolationists, planned to publicly declare that war would be ruinous to the United States and that he was the only one to stop it — and prevent a third term for Roosevelt. Apprised of the plan, Roosevelt summoned the ambassador to the White House before Kennedy’s expected meeting with his co-conspirators. Over dinner, the president pressured Kennedy into giving a radio address lavishing praise on Roosevelt, a leader so perfectly suited to the challenging times that there should be no thought of electing anyone else. Overpowered, Kennedy’s only choice afterward was to resign. “At the end of the day, Roosevelt needn’t do a thing to slay his dragon Kennedy,” Ronald concludes. “Joe had done it himself.”

It was a stunning fall from grace, yet I felt curiously unmoved by this retelling of it. In Ronald’s hands, Kennedy feels distant. Sometimes he completely disappears for pages in favor of dense European history. I also found some textual quirks irritating. Is the subject of the book “Joe” or “Kennedy”? Ronald uses them interchangeably, sometimes in the same sentence. At other times, I couldn’t sort out which Kennedy — Joe Sr. or Joe Jr. — was espousing casual antisemitic views. I had to turn to Ronald’s notes or the Internet to clarify. And I was constantly put on alert by Ronald’s tendency to state things in absolute terms — “Joe was called ‘Daddy’ by the girls and ‘Dad’ by the boys” — only to quote a contradictory primary source pages later: “Kick’s April 15, 1936 letter to ‘Dearest Dad.’ ”

The publicity claim that the book would reveal “the truth” about Kennedy seems an overreach. I kept waiting for a bomb to drop, but the unflattering truths that Ronald reveals, particularly those of Kennedy’s disastrous two years in London, have been known for at least a generation. In 1987, Doris Kearns Goodwin introduced much of this material in “The Fitzgeralds and the Kennedys.” The definitive volume “The Patriarch: The Remarkable Life and Turbulent Times of Joseph P. Kennedy,” by David Nasaw, was a finalist for the Pulitzer Prize in biography a decade ago. And just this month, Jane Karoline Vieth published “Tempting All the Gods: Joseph P. Kennedy, Ambassador to Great Britain, 1938-1940,” a subject she has been writing on for decades.

Kennedy’s brief ambassadorship opened a window on his family’s saga by revealing the extravagant character of the patriarch. What Kennedy put in motion, in Ronald’s estimation, was a “familial recklessness and competitiveness which killed one son and led to the death of two others.” The origin, in other words, of the “Kennedy curse.”

The Ambassador

Joseph P. Kennedy at
the Court of
St. James’s, 1938-1940

By Susan Ronald

St. Martin’s.
441 pp. $29.99