Love letters between the 29th U.S. President Warren Harding and his mistress were released by the Library of Congress after the expiration of a 50-year court seal. (Reuters)

Love letters between the 29th U.S. President Warren Harding and his mistress were released by the Library of Congress after the expiration of a 50-year court seal. (Reuters)

On Christmas Eve, 1910, future president Warren G. Harding got out a photograph of himself, and on the back wrote an impassioned love note to his mistress.

“My Darling,” he began. “There are no words, at my command, sufficient to say the full extent of my love for you — a mad, tender, devoted, ardent, eager, passion-wild, jealous . . . hungry . . . love . . .”

“It flames like the fire and consumes,” Harding, 45, who was married and would be elected the 29th president a decade later, wrote. “It racks in the tortures of aching hunger, and glows in bliss ineffable — bliss only you can give.”

His lover, Carrie Fulton Phillips, 37, who was married to one of Harding’s friends, kept the missive and began keeping dozens more love letters from Harding — some of them 30 pages long — despite his requests that she burn them.

Held at The Library of Congress under court-ordered seal for the last 50 years, the trove of the original, often-juicy letters is scheduled to be opened to the public via the Internet on July 29.

The library is hosting a program to discuss the collection July 22, featuring library and outside experts and a Harding descendant.

The roughly 900 pages illuminate an extraordinary and intimate chapter in the life of a seemingly drab president who was dogged by political scandal, died in office and had campaigned on a platform of “a return to normalcy.”

The unsealing of the letters comes two months after a collection of private letters of Jacqueline Kennedy was pulled from auction.

Kennedy’s letters were those she sent to a confidant, a Roman Catholic priest in Dublin, over the course of 14 years. They were withdrawn from auction after the Kennedy family objected.

The original Harding letters were sealed July 29, 1964, the library said. The Harding family donated them to the library in 1972, with the stipulation that they stay sealed until July 29, 2014.

But forgotten microfilm copies were discovered in an Ohio historical repository a decade ago by an author researching the president, and he used many of them in a detailed but little-known book.

The letters reveal, among other things, an insecure, romantic man who sometimes wrote his mistress in code and slipped away for secret meetings with her in Germany, England and Canada.

They met in New York and had assignations on an ocean liner, where they began the day “with glorious kisses and fond caresses, and you were so superb,” Harding reminisced later.

He came up with code names for them. Sometimes she was “Sis” or “Mrs. Pouterson.” He was “Jerry.” Together, they were “the Poutersons.”

And there is little doubt about what went on.

On Jan. 2, 1913, he wrote:

“My Carrie, Beloved and Adored. . . . I do love you so. . . . I wonder if you realize how much — how faithfully, how gladly . . . how passionately. Yes you do know the last, you must have felt the proof.”

On Sept. 15, 1913, he wrote her, recalling an especially amorous weekend in New York:

“I do not know what inspired you, but you . . . resurrected me, and set me aflame with the fullness of your beauty and the fire of your desire. . . . imprisoned me in your embrace and gave me transport — God! My breath quickens to recall it.”

Two months later, he wrote his love for her was “the surpassing influence of my life. It is big, and glorious, and hallowed. It is full of blessings and radiant with dreams. It could be as ardent and wild and impassioned as you have ever known it.”

Harding’s affair with Phillips began in 1905, according to James David Robenalt, an Ohio attorney and author, whose 2009 book, “The Harding Affair: Love and Espionage During the Great War,”details the relationship.

The book also reviews suspicions that Phillips spied for the Germans during World War I.

And it reproduces many of the love letters.

Robenalt, who e-mailed a few more of the letters Thursday, had stumbled on the bootlegged microfilm of the correspondence.

“When I first read these, I felt like a voyeur,” Robenalt said in a telephone interview Thursday. “I shouldn’t be reading this. I should look the other way.”

Harding and Phillips both seemed to be in barely functioning marriages. His wife, Florence, who was divorced from her first, alcoholic husband, was chronically ill, Robenalt recounts.

“There isn’t one iota of affection in my home relationship,” Harding wrote Phillips in 1913. “It is merely existence, necessary for appearance’s sake.”

Robenalt said, “I believe, based on everything I’ve read of these 900 pages, that [Harding’s relationship with his wife] was sterile, and that Carrie was his sexual outlet.”

For her part, Phillips chose to live for months in Europe with her daughter and away from her husband, Jim.

Robenalt wrote that it’s not clear what sparked the romance. Harding was a big, handsome, presidential-looking man. Phillips was “beautiful, ample . . . and strong willed,” Robenalt recounted.

Both families had lived in Marion, Ohio, and knew each other.

The affair went on while Harding, a Republican, served as Ohio’s lieutenant governor and later a U.S. senator, the Library of Congress said.

“It was troubled and problematic,” Robenalt said. “But boy, oh boy, was it steamy.”

“This woman was clearly the love of his life,” Robenalt said. Although Harding is rumored to have had other affairs, “I don’t think he was a rampant womanizer,” Robenalt said. “I think he fell in love with women.”

By the time of Harding’s presidential inauguration in 1921, the affair with Phillips had ended.

Years before, in 1913, he seemed to become uneasy about the letters he had sent her.

“I have been thinking about all those letters you have,” he wrote her on Jan. 2, 1913.

“I think you [should] have a fire, chuck ’em! Do. You must. If there is one impassioned one that appeals to you, keep it . . . [but] please, chuck the extra pictures, letters and verses. They are too inflammable to keep.”

Robenalt said Harding probably got a thrill out of just writing to Phillips. “A lot of his letters are sexual-fantasy letters,” he said. “Clearly, this is his sexual outlet, in part, writing to her.”

But Phillips didn’t burn the letters.

Harding died of a heart attack on Aug. 2, 1923 in a San Francisco hotel during a cross-country political tour, exhausted and tainted by the famous Teapot Dome bribery scandal involving his secretary of the interior.

The nation was stunned by his death — thousands of people lined the train tracks as his body came back to Washington — and he and his wife were eventually buried at a grand, columned memorial in Marion. She died in 1924.

Phillips had returned to Marion. Her husband died in 1939. She died, suffering from dementia, in a state-run nursing home in Marion in 1960.

When her lawyer went through her decrepit, old house before her death, he broke open a locked closet door and found the cache of love letters, according to Robenalt.

Over the years, they passed through several hands, and after some litigation over ownership, they went to the library.

But a microfilm copy wound up in Cleveland’s Western Reserve Historical Society, according to Robenalt’s book.

In 2004, conducting research for an upcoming symposium, Robenalt called the society in search of Harding memorabilia, he said. An archivist said the society had some and urged Robenalt to come see it for himself.

On arrival, Robenalt said he was taken into a back room. The door was closed and a box produced.

“Do you know who Carrie Phillips is?” archivist asked, according to Robenalt.

“Sort of,” Robenalt said he replied.

“These are the love letters,” the archivist said.