I began reading this book fully expecting it to affirm my pre-existing low opinion of its protagonist. I finished it persuaded that Joseph P. Kennedy was easily the most formidable and most interesting member of the clan that owes its prominence in American life to his shrewd and unstinting exertions.

Let us not confuse formidability with likeability or virtue, however. As David Nasaw, professor of history at the City University of New York, makes clear in this extraordinarily fine biography, Kennedy was a man of many parts, few of which make him a prospective candidate for canonization.

Ruthless, energetic, charming when he wished to be, Kennedy possessed an astonishing aptitude for making money, whether in good times or in bad—of that there can be no doubt. As a corner-cutting entrepreneur, he was typically three steps ahead of his nearest competitor and barely three inches this side of the law. Yet he wanted more than money. He wanted power. And for his family—perhaps too for his coreligionists—he wanted status and recognition.

So when business needed policing—that is, when regulating Wall Street meshed with his own ambitions without threatening his financial position—Kennedy transformed himself overnight from business buccaneer into scourge of plutocrats, unhesitatingly accepting Franklin Roosevelt’s 1934 invitation to chair the newly created Securities and Exchange Commission. He filled that post with distinction. Yet upon stepping down a year later, he wasted no time offering his services to large corporations, enriching himself further by tutoring them in how to evade the rules he himself had put in place.

In sharing the fortune that he amassed, Kennedy demonstrated unfailing generosity. He entertained friends—especially the well-heeled and the well-connected—lavishly. He supported a long list of worthy causes, many of them affiliated with the Catholic Church. In return, he expected nothing—apart from slavish loyalty. Woe betide the individual or institution giving the wrong answer when asked to do some small favor for one of the benefactor’s many offspring.

Kennedy loved and doted on his children, albeit usually from a considerable distance since he was seldom actually at home. Long stays spent recharging his batteries at his Palm Beach retreat or in some palatial rental on the coast of France formed an essential part of his routine. For paterfamilias, R and R meant hanging around with pals and palling around with women not his wife—better for Rose and the kids to entertain themselves elsewhere.

To outsiders, any long-lasting marriage contains elements of mystery. The union between Joe and Rose remains inexplicable. Apart from impregnating his wife, Kennedy spent remarkably little time in her presence. To mark their twentieth wedding anniversary, for example, he gave Rose a trip to Europe, a typically munificent gesture. Equally typical is the fact that she took the trip without her husband, who remained stateside. Still, whenever they were apart, Joe routinely sent his wife chatty and affectionate letters. The children too, off at boarding school or cared for by watchful nannies, received from their absent father frequent missives filled with encouragement, advice, and gentle counsel. They adored him.

Catholicism formed an indelible part of Kennedy’s identity. On Sundays, he attended Mass and received Communion. On Fridays, he abstained from eating meat. On a regular basis, he partook of what was then called Confession—a good thing given that his cavorting with mistresses ranging from Gloria Swanson to Clare Boothe Luce presumably provided plenty to discuss when he entered the confessional.

Students of American foreign relations will take a special interest in Nasaw’s account of Kennedy’s tenure as ambassador to the Court of St. James. His appointment to the position in 1938 marked his arrival at the apex of public life. British papers delighted in recording the doings of the glamorous and photogenic Kennedys (for once, parents and children were living under the same roof). Back home, meanwhile, pundits were touting Joe as a potential president. Yet by the time he left Great Britain in late 1940, his reputation had sustained irreparable damage and his public life had all but ended.

In life, all sins are forgivable. In politics, some are not. Ambassador Kennedy committed the unforgivable sin of getting World War II wrong. He arrived in London determined to help prevent the recurrence of another catastrophic European war, a goal to which FDR likewise subscribed. Any such war, Kennedy feared, would inevitably involve the United States and would put members of his own family at risk. Although events proved him right on both counts, his enthusiastic support for Neville Chamberlain’s policy of appeasement and his stubborn opposition to U.S. intervention even while Hitler was chalking up one victory after another marked him for all eternity as an “isolationist.”

For once, Kennedy demonstrated an inability to adapt. As international circumstances changed, the political chameleon in the White House adjusted his views. In failing to conform to the evolving position of his political patron, who as late as November 1940 was solemnly, if less than honestly, promising to keep the United States out of war, Kennedy committed a fundamental error. Once a trusted envoy and Roosevelt intimate, he became an embarrassment. Reviled in London and increasingly ignored in Washington, the ambassador found himself a virtual persona non grata. It was a humiliating fall from grace.

By the time the United States actually entered World War II, Kennedy himself was finished politically. Still, there remained plenty more money to be made. And, of course, the story of the Kennedy family had only just begun. In the long second act that followed, Kennedy’s sons achieved with their father’s backing much of what he had hoped for his family, even as Kennedy himself endured the tragedies that fell with cruel regularity like a hammer’s blows.