Mary Anne Disraeli was a lot of fun at dinner parties. But she was no one’s idea of a model political spouse, in either her time or ours. The wife of Benjamin Disraeli, 19th-century Britain’s most important conservative politician, Mary Anne prattled on nonstop—“very vulgar,” Queen Victoria thought upon first meeting her. On one occasion, Mary Anne unleashed such a torrent of talk about the 32 marriage proposals she had purportedly received that the unfortunate man seated next to her had no chance to eat. At glittering dinner tables, she made flirtatious references to her “Dizzy” in his bed and bath.

Twelve years older than her husband, Mary Anne Disraeli favored a look that was as eccentric as her spicy conversation. Well into her 70s, she wore the outfits of an ingenue: a wreath of red feathers or a pink-satin dress heaving with lace, and always piles of diamonds, gleaming from her earrings and necklaces and, for formal occasions, sewn onto her sleeves and studding her tiaras. Scandal clung to her. Had she and Benjamin been carrying on before her first husband died? What about those washed-up rakes (the “corpulent beau, or seedy second rate dandy,” in her soon-to-be second husband’s description) who had once paid her evening visits?

Mary Anne was a liability to Benjamin Disraeli, but she was also—oddly—the making of him, as Daisy Hay’s accomplished new biography of the pair, Mr. and Mrs. Disraeli: A Strange Romance, illustrates. Without his wife, Disraeli might well have failed at politics just as he had made a hash of all his previous endeavors. In Hay’s telling, “they themselves spun stories around their partnership, but they also made the tales they spun come true.” As an earlier biographer, the British historian Jane Ridley, aptly put it, Disraeli “was a genius, but he owed his success to Mary Anne.”

Few political unions today would earn such high marks. By now, the spectacle of connubial dysfunction in elected office has achieved its own sort of dreary protocol, the details changing but the composite firmly fixed. The cheating husbands and their jilted wives, the pallid denials and the unconvincing contrition, the trembly lips and pained expressions: Bill and Hillary Clinton, Newt and Marianne Gingrich, Eliot Spitzer and Silda Wall Spitzer, Mark and Jenny Sanford, Anthony Weiner and Huma Abedin—and that’s just for starters. So unremarkable is the moral trespass that all the talk is of the practical consequences. Will she stand by her man? Will he be reelected? What price does a politician pay for personal disloyalty?

At glittering dinner tables, Mary Anne Disraeli made flirtatious references to her “Dizzy” in his bed and bath.

We’ve lost sight of a different question, at once novel and quaint, which in the United States will soon move to the foreground. What about a politician’s loyalty to his or her disreputable spouse? The Disraelis’ story demonstrates how a politician’s devotion, even to an apparently damaging partner, can be turned to advantage, especially if the politician stands accused of opportunism or treachery. In the case of Hillary Clinton, that Victorian story may be especially illuminating. To understand how a spurned first lady can metamorphose into a presidential front-runner, let us follow one mastermind into the thicket of 19th-century marriage and politics.

When Mary Anne Lewis met Benjamin Disraeli in 1832, there was nothing to signal his genius other than his own grandiosity. She was 39 and had married well, if not happily: her spouse was a businessman turned member of Parliament. Disraeli was 27 and had already tried his hand at lawyering, stock-market speculating, and the newspaper business before publishing a novel scrutinizing London society, which reviewers hated. Baptized as an Anglican at the age of 12 when his father broke with the family’s synagogue, Disraeli was an outsider. He cultivated self-consciously Byronic passions, styling his hair in black ringlets, donning purple trousers with scarlet waistcoats, and wearing his rings on top of white gloves. He had accumulated a mountain of debt.

Less than four decades later, Benjamin Disraeli was the prime minister of Britain. He had remade the Conservative Party in line with his own political philosophy, championing Britain’s traditions and the glory of its empire. He orchestrated a massive expansion of the franchise that nearly doubled the number of Britons eligible to vote, and he embarked upon a legendary feud with that other presiding genius of British politics, the Liberal William Gladstone. Disraeli also wheedled his way into the affections of Queen Victoria, who as a personal favor to the prime minister granted Mary Anne the title of viscountess in her own right.

Most biographers of Disraeli have tended to treat Mary Anne at best as a bit of a joke, and at worst as an impediment to his advancement. Certainly, Mary Anne was a rich widow, her first husband dead little more than a year when she and Disraeli wed in August of 1839. Mary Anne’s money helped Benjamin stave off the creditors who trailed after him. And her vivacious campaigning on his behalf in Shrewsbury, where he stood for Parliament, helped him secure a seat. She gaily chatted up the townspeople, and threw flowers into the crowd as her husband proceeded through the streets. “You never can have a dull moment, Sir,” remarked an appreciative voter. But so vast were Benjamin’s debts that Mary Anne’s funds hardly covered the interest to his creditors. He had to rely on other rich widows, especially the octogenarian Sarah Brydges Willyams (like him a convert of Jewish origins), and a friend, the financier Lionel de Rothschild, to bail him out once and for all. As for Mary Anne’s campaigning, charismatic though she may have been, there were plenty of other female charmers out stumping for candidates, and many political wives far more adept than she at forging advantageous alliances.

For Daisy Hay, who has also written a biography of the Shelleys and their circle, the key to the Disraelis’ partnership was the drama of romance they constructed around themselves. Born into a world of stories, as novel-reading joined the theater as the century’s dominant forms of entertainment, the couple understood the potency of reinvention, the ability of ordinary people to imagine a life of greatness and conjure it into being. How lucky they were, Disraeli exulted, to live in an age of “infinite Romance”: “the most powerful people in the world, male & female, a few years back, were adventurers, exiles, & demireps.”

Disraeli used his personal story, framed by his grand passion for Mary Anne, as a political tool—mandatory in our day, but an innovation in his. His protectiveness and constancy in the face of her social gaffes and oddities took on the status of legend: “Love me, love my Mary-Anne,” he said, and he meant it. When his most powerful political ally, the Conservative prime minister and grandee the Earl of Derby, taunted Mary Anne for the amusement of his dinner guests, Disraeli left Derby’s house the next day, never again to visit him at home. To the callow friend who asked why he remained with his wife, Disraeli responded, “There is one word in the English language of which you are ignorant … Gratitude.” Even the stories about Mary Anne’s worshipful devotion underscored his solicitude. “I am sorry when he is in office,” she told one young man seated next to her at a dinner, “because then I lose him altogether, and though I have many people who call themselves my friends, yet I have no friend like him.”

Loyalty to Mary Anne mattered so much to Disraeli’s success precisely because he was an outsider and an upstart. His position was in many ways preposterous: a converted Jew defending the sanctity of the Church of England, a dandy on the make leading a party of country gentlemen. On his climb up the “greasy pole,” as he famously characterized politics, Disraeli had shoved his rivals and betters down. He stood accused (not unjustly) of opportunism, even treachery. To these charges, his devotion to Mary Anne served as a counterweight, a means of rehabilitating himself. Disraeli’s loyalty to his wife was, or seemed to be, what was genuine about him: even his arch-antagonist, Gladstone, was touched by it.

Thus did marital loyalty, against the odds, help to redeem a reputation for unscrupulousness in politics. Just as infidelity in private serves to indict a politician’s character, so, too, can fidelity in public burnish it. The catalyst in Hillary Clinton’s transformation from controversial first lady to politician with her own ambitions was her steadfast conduct amid the Lewinsky affair. Although skeptics at the time speculated about her motivations, Clinton’s allegiance to her husband won her public adulation and may have helped save his presidency. After the House impeachment, her approval ratings skyrocketed to an all-time high.

Like the Clintons’ saga, there was, inevitably, more to the story of Mr. and Mrs. Disraeli than met the eye of a rapt audience. Hay handles the ambiguities of their relationship, through all its twists and turns, with subtlety. The second act of their marriage was unsettled. “Pas content,” wrote Mary Anne in her account book as the couple led increasingly separate lives. There were quarrels; Disraeli spent nights fuming in hotel rooms and, possibly, having affairs. But a happy third act followed. To celebrate the expansion of the franchise—his great political triumph—Disraeli slipped away from his jubilant supporters and went home to his wife. Mary Anne was waiting for him with a Fortnum & Mason pie and a bottle of champagne. “Why, my dear, you are more like a mistress than a wife,” he exclaimed to a delighted Mary Anne. “As for our enamoured sexagenarians,” Disraeli later wrote, “they avenge the theories of our cold-hearted youth.”

When Disraeli asked Queen Victoria to confer a peerage upon Mary Anne, his wife was likely already sick with the cancer that would kill her in 1872. On a cold and wet day in December of that year, Disraeli watched her coffin being lowered into the grave. Bareheaded, he stood in the rain for a full 10 minutes. He was brokenhearted and drained—but was he also counting the minutes? He would fall in love again that next summer, continue writing novels, and enjoy a second stint as prime minister. For the true political animal, perhaps romance is merely the continuation of politics by other means. What turned the Disraelis into a power couple for the ages was their ability to make their outsize love affair seem real, even to themselves.