A while ago, I stumbled upon a photograph of President James Garfield and his young daughter Mollie. (You can see it here.) Even though it was taken in the 19th century, a time when just about everyone looked stern in front of a camera – maybe because exposures lasted forever – Garfield appears to be positively delighted.

Are his eyes filled with humor because he's about to tell a joke? Is he just ecstatic to be spending time with his daughter, who's giving the evil eye to someone outside the shot? Or is that grin hidden under his beard just a sign that he's a jolly guy?

Whatever the case, the photo hints that Garfield was a remarkable man. Destiny of the Republic: A Tale of Madness, Medicine and the Murder of a President, one of last year's top bestsellers, confirms it.

"Destiny of the Republic," which our reviewer Erik Spanberg wrote brings back to roaring life a tragic but irresistible historical period," is now out in paperback. I contacted author Candice Millard, who previously wrote the bestselling "River of Doubt" about Theodore Roosevelt's treacherous African trip, to ask about the reaction to the book and what she found when she looked into the fascinating life of this most obscure of presidents.

Q: How did you come across the little-known story of President Garfield?

A: I came in to this book without an interest in Garfield. I didn't know anything about him other than he'd been assassinated.

I was actually interested in Alexander Graham Bell and looking at a book with a lot of science in it. I stumbled upon the story of him trying to find the bullet in Garfield.

I wondered why Bell would do this. He's young, he just invented the telephone a few years ago, and he abandons everything he's doing to work night and day on an invention. I start researching Garfield, and I'm blown away by how brilliant he was and the huge heart he had.

It took me three years to work on the book, two years of doing research, and I was far into it by the time I wrote his death scene. I called my husband in tears.

I didn't want to write it. That's ridiculous: It's been 130 years since he died. But I felt like I knew him. I cared about him, and I admired him, and I was surprised by all of that.

Q: Four presidents have been assassinated, but we remember just two: Lincoln and Kennedy. Why have we forgotten Garfield?

A: We forget because it's been so long since his assassination, and he was in office for such a short time.

It was interesting to me in the National Museum of Natural History they have a little alcove about presidential assassinations. Fortunately for Garfield he's right across from Kennedy. But when I was there one day, I'd watch people come in, and they'd look at Kennedy and Lincoln and leave. They'd never turn around to see anything.

We forget, and we don't know the tremendous tragedy this was for the country at this time.

Q: What made him unique as a leader?

A: He was trusted, and he's really the first president since the Civil War to be accepted by the whole country as its leader. The assassination was shocking and devastating.

Q: He was a major advocate for black people, wasn't he?

A: From a very young age, his religion was the Disciples of Christ, and they were fierce abolitionists. He cried when John Brown was hanged, hid a runaway slave, and was a staunch fighter in the Civil War and a hero in the Union Army.

For him, it was mostly about abolition, and he was instrumental in bringing about rights for freed slaves after the Civil War, including suffrage.

During his inaugural, freed slaves were openly weeping in the crowd. A party of 600 black men formed after his assassination to lynch the assassin, Charles Guiteau.

Q: Some presidential rankings don't include him because he was only in office for a few months. But those that do typically rank him toward the bottom. Is that fair?

A: It's unavoidable. He was in office for only four months, and I think that's the reason for that.

But he was in Congress for almost 18 years. And what he accomplishes in four months is to defeat arguably the most powerful and most corrupt man in the country, Senator Roscoe Conkling, by sticking to his own ideals and believing in himself.

What makes him very rare was that he was his own man. I can't think of another presidential candidate, at least in recent times, who didn't hunger for the presidency. He didn't have presidential fever.

At the Republican National Convention, he didn't want to be a candidate but to give a nominating address for another man. He found himself thrust into this role, and never had to compromise his own values and ideals along the way. He was his own man as president, and that would have made him very powerful.

Q: The assassin, Charles Guiteau, is a fascinating character in this own right, a deranged stalker who kept pestering the White House for a job. What did you learn about him?

A: He was delusional and mentally ill. He had been for a long time, and should have not been near anyone, let alone the president.

It was a time when people could sort of slip away. His family tried to have him institutionalized, and he'd disappear. He'd move from city to city, skipping out on his bills, and being very isolated and on his own. He lived in his own foggy, deluded mind, becoming more obsessive.

He believed he would personally make Garfield president by delivering the speech he'd written, and then, through gratitude, Garfield would make him ambassador to France.

He became more obsessive and desperate. He went to the White House and Department of State every day.

Q: Why didn't Garfield have better security?

A: There were all these assassinations going on in Europe, but people believed that's because they had these monarchies. They truly did not believe this would happen again. They didn't want any distance set up between them and their leader; they thought that's something for monarchies and kings.

One night, Guiteau follows Garfield and his secretary of state all around the city. They have no protection, and Guiteau is holding a loaded gun.

Q: It's amazing how this random person actually had direct access to the president and to the secretary of state, who eventually got so frustrated that he told him to get lost. How did that happen, just a couple decades after Lincoln was shot?

A: People believed even if they didn't have any experience or credentials they should be able to make their case directly to the president about getting a job.

It was a nightmare for Garfield. He had to spend 10:30-1:30 every day meeting one-on-one with office speakers.

Q: Guiteau's defense at trial was that he was insane. What can we learn from our debate today over the insanity defense?

A: Guiteau's was one of the earliest insanity defenses. If anyone should have gotten off, it was Guiteau, but the country was determined to see him pay.

Because he was he was delusional, he loved all the attention he was getting. He gave every interview he could, so I could be in his mind.

You can see this horrible danger coming toward this young president who has so much promise and life ahead of him. You see this threat coming, and there's nothing you can do to stop it.

Q: Has the reaction of readers surprised you?

A: When you write about Theodore Roosevelt, you've got a built-in audience. I knew I was taking a real chance writing about Garfield. It was thrilling to see that there was an interest, that people would give it a chance.

Q: Are readers falling for him?

A: They seem to be. When I go out and talk, I get big audiences, and people seem very enthusiastic. I follow things on Twitter, and every one in a while I'll see the hashtag #garfield2012.

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Garfield was brilliant and had a heart to match his mind. People respond to that.

Randy Dotinga is a regular contributor the Monitor's Books section.