Americans remember Franklin Delano Roosevelt as the president who led the country through the Great Depression and World War II. He bolstered the nation's spirits with his confidence, strength and optimism, despite being crippled by polio, a disability that's largely invisible in photographs and newsreels of his presidency.

But historian James Tobin says, despite misimpressions to the contrary, Americans of Roosevelt's day were well-aware of his disability. In fact, Tobin says, Roosevelt's struggle to overcome his affliction was an important part of the personal narrative that fueled his political career.

Tobin tells Fresh Air's Dave Davies, "[Roosevelt] only discovered who he really was through the ordeal of polio. ... It gave him a kind of confidence in his own strength that perhaps no one can have until you're tested."

Roosevelt contracted polio at the age of 39, and Tobin's new book explores his battle with the illness and the ways it molded his character and influenced his rise in the Democratic Party. Tobin has written previous books about the Wright brothers and war correspondent Ernie Pyle. His new book is The Man He Became: How FDR Defied Polio to Win the Presidency.

On how good sanitation made kids more susceptible to polio

Before the polio vaccine, pretty much every little kid ingested the polio virus but was protected by maternal antibodies, so even though the virus passed through his or her system, they wouldn't become sick with disease. As sanitation got better, they had fewer immunities, and so if the virus did creep into a community with good sanitation, kids were more likely to get sick and to become seriously ill.

Roosevelt had grown up on an isolated estate in upstate New York. He probably had immune deficiencies to begin with — he was always getting sick with one bug or another. So he was particularly susceptible when, even though he was an adult, he contracted the virus.

On FDR's recovery efforts

Roosevelt went into a long period of physical rehabilitation after recuperating for several months. By December 1921, he was ready to have a physical therapist begin to massage his muscles, begin to work his muscles, begin to try to figure out exactly the extent of the damage. As more and more time passed in the coming weeks and the early months of 1922, he was able to begin to exercise on his own. This was laborious, difficult: He really could not even stand up on his own at all for months and months, and so this was a matter of lying in his bed, performing these minute little exercises, trying to move one muscle and then another muscle. ... It was painstaking, it was difficult. He had to have his legs put into casts at one point to prevent against contractures. ... It was really a grueling process.

On misimpressions of FDR's openness about his condition

When I've talked to people in the past ... I've always asked them, "Did you know about FDR's condition?" And they've always said yes. What they say is, "We realize later that he was more disabled than we knew, but we certainly knew he was disabled, we knew that he couldn't walk." I think that this misimpression comes from a couple of things:

There was a book published in the 1980s called FDR's Splendid Deception in which the writer, Hugh Gregory Gallagher, I think overstated the evidence for FDR covering this up. And then in the debate over the Roosevelt memorial in Washington that took place in the 1990s, that theme got repeated over and over again by various advocates in that argument. And then it got put into a couple of television documentaries, and so it just had a viral effect.

All you have to do is go back to the newspapers of the time, especially from the 1920s when Roosevelt was making his political comeback, and his disability was discussed constantly. He was very frank about it. So there's no question that people knew about it. And you see during his presidency, people who were themselves disabled, people who had polio, their children had polio, writing to FDR in the White House by the hundreds and talking about his disability. The March of Dimes [nonprofit] itself, which came about during Roosevelt's presidency, he was the leader of it, was an effort to fight polio. The polio campaign that was waged every year had Roosevelt as its figurehead.

On how FDR's condition affected his marriage to Eleanor

I think at first the polio brought the two of them closer together. It was only a few years earlier, 1918, that Eleanor Roosevelt had discovered that he had had this affair with her own social secretary, Lucy Mercer, a situation that everyone knows about. So the marriage had been deeply damaged. Her trust for him had been destroyed.

But polio sort of called upon her to give him all the care that she possibly could give him. That was the sort of wife that Eleanor saw herself as: somebody bound by duty to help her husband. And she absolutely did for many months. She cared for him, she sort of organized his care with physical therapists and nurses at the same time that she was looking after five children and a couple of different households. She really did devote herself to his case.

As he began to pursue his recovery in other places where he could go for treatment, she increasingly saw that she couldn't devote the rest of her life to him and didn't care to. She wanted to express her own individuality, and she wanted to pursue a position of politics of her own, and so she increasingly did that. After 1922 into 1923, they began to lead separate lives, supporting each other in what they were doing but acknowledging they were no longer the kind of husband and wife that they had been before his affair.

On how Roosevelt worked around his condition

Roosevelt realized that when you were crippled — and that was the word that he would use — you have a tendency to make people uncomfortable. People don't know what to say, they don't know where to look, they don't know how to treat you, they don't know whether to feel pity for you, when pity is the last thing that you want. ...

He had to persuade people to feel comfortable in his presence. ... [The therapists and he] began to work on his gait, to work on the way he would walk with the canes and crutches and assistance he would use. So his walk, although slow, began to look more and more natural. And he would seat himself, and he would throw up his head, he would begin to talk — he was always talking, actually — to put people at ease. And this whole physical routine that he developed of putting people at ease was enormously effective, and it made people forget that he was disabled.

On FDR using his disability as a political advantage

[In a speech in Rochester, N.Y.,] he was talking about the needs of disabled children in the state of New York and he mentions himself. He says, "I myself have been through this ordeal, and I am a symbol of what can happen when people with disabilities are strongly supported."

And nobody had expected him to say this out loud; nobody had expected him to address this issue in this way, to turn the disability on its head and make it into this advantage. And so it had [an] electrifying effect on the audience. ... I think Roosevelt ... realized this was a strong part of his presence as a candidate, and it was something that actually appealed to people.

On whether his disability made him a better president

Certainly people close to him said it tempered him. Eleanor herself said it made him stronger and more courageous.

That doesn't quite make sense to me. I think people have those innate capacities or they don't. The crisis draws it out of them. It allows them to see who they really are. And that's why I chose the title The Man He Became. I think he was that man before he became sick, but he only discovered who he really was through the ordeal of polio. So it gave him a kind of confidence in his own strength that perhaps no one can have until you're tested.

I also think it inevitably gave him a kind of passion for people who are suffering that he couldn't have had if he had not deeply suffered himself. That capacity was perfectly timed for the country's problems in the Great Depression.

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