Seventy-five years ago, the president of the United States arrived in Salt Lake City for a speech at the Tabernacle. Warren G. Harding and his highly influential first lady, Florence, were in the midst of a grueling 5,000-mile "Voyage of Understanding."

Forty-four days after the tour began, the president died.The trip began in Kansas City, Mo., on July 2, then Harding, who had a weak heart, traveled on to Colorado Springs, Colo., where he spoke of spiritual things - like faith and the problems of materialism.

At the first lady's urging, the Hardings diverted their trip and headed to Zion Park in Springdale, Utah. Utah's Sen. Reed Smoot had converted Florence Harding to the proposition that the park's beautiful boundaries should be expanded and declared a national park.

She said, "Warren, we're going to take that trip," even though it was an extra 350 miles by train and car.

At Zion, she gave speeches while the president got his only escape from political business by horseback riding along the Virgin River. Since Harding died before the state park could be expanded into a national park, the task was left to Calvin Coolidge to finish - but it was Florence Harding who engineered it.

On July 11, the presidential party arrived in Salt Lake City, where members stayed at the Hotel Utah and Harding spoke at the Tabernacle. Carl Anthony, a historian of first ladies, is now retracing the presidential tour and speaking at all the same sites Harding visited.

Anthony's biography, "Florence Harding," is an important book designed to re-evaluate this first lady and to throw new light on President Harding.

In a wide-ranging telephone interview, Anthony said Harding "got an incredible response" from his Salt Lake speech, probably the best of his tour, but "he was physically listless and lacked his usual fireworks."

It was in Salt Lake City that the traveling press decided Harding was slipping. It was also here that Harding, under pressure from his wife, publicly affirmed that he would never touch liquor again.

Even though Prohibition was the law of the land, Harding had been a heavy drinker, and the first lady served liquor in the White House.

Afterward, the president forged on to Alaska, then to Vancouver, Seattle, Tacoma, Portland and Eugene. In San Francisco, the president passed away of heart failure and food poisoning, prompting false rumors that Florence had poisoned him.

Anthony says a belief in astrology and the supernatural was her "Achilles heel." She believed that trip was cursed, a claim based on her astrologer's prediction that Harding would not survive for a second term.

Anthony is convinced that Florence Harding was a charismatic, forceful woman who helped make her husband president, then jumped into policymaking.

Anthony says "The Duchess," as she was called, was so indispensable to Harding in the presidency that she deserves as much attention as Eleanor Roosevelt.

Since high school, Anthony has been interested in American presidents. As a history major at George Washington University, he was struck by the realization that "no one had really made an assessment of the balance of power in their marriages and taken an accounting of the political influence of first ladies."

Anthony decided to take on the job. He is frustrated by claims that such influential first ladies as Nancy Reagan and Hillary Clinton took powers no first lady had ever had before.

He believes that Florence Harding, like Eleanor Roosevelt, "really consciously set out to use power in the presidency." Other first ladies, says Anthony, had used the office in a civic way, Nellie Taft with cherry blossoms, Ellen Wilson with Washington, D.C., slum clearance.

"But Florence Harding was the first to develop a national constituency for which she could be a national voice - the disabled veterans of the First World War."

Anthony doesn't believe in the supernatural. But his work is especially notable for the rich sources he almost miraculously located and utilized in his interpretation.

He was able to unearth Florence Harding's hand-written diary from an Ohio barn sale; he obtained transcripts of Warren Harding's love letters and erotic poems to Carrie Fulton Phillips, his Ohio mistress, and transcripts of conversations between Evelyn McLean, Florence's best friend, and Boyden Sparkes.

All these sources are extremely revealing about the nature of the Harding marriage, his numerous, unquestioned infidelities, and the role Florence played in her husband's work. Her diary, especially, revealed her rage and bitterness at her husband's adultery.

"You see in her character," says Anthony, "the evidence of the independent woman, feminism, suffrage, and the call for equal rights, although at the time she never felt she was part of any movement."

As Harding's health deteriorated, says Anthony, she would fill in for him - by popping up on the back platform of that train when they were expecting to see the president. One reporter referred to her as "the acting president."

Anthony believes President Harding probably suffered from what is known today as sex addiction. Even during this famous trip, when his health was failing, Harding was still flirting with young women.

Florence scolded him in front of the press, saying, "It took you as long to get through 3,000 tourists yesterday at Old Faithful as it did to say hello to those waitresses."

In spite of Harding's corruption, Anthony believes the time has come to assess Harding "the whole person" and see him as a man of strengths as well as weaknesses.

"I hope the book will help change that perception of Warren Harding, although my great goal is to drastically change the perception of Florence Harding."