It was Roosevelt's battle with polio in his 30s that gave him insight and empathy, he continued.
"He finally came to appreciate life as seen through the eyes of others," Gergen said, "and it gave him a confidence in what we could become as a people."
Gergen compared the country's situation today to that of 100 years ago.
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"It's important to remember that at the start of the 20th century, we began with the same hopes but then plunged into the bloodiest wars in history," he said.
This was the fault of a few leaders "who led us astray," Gergen explained. "The quality of individuals does matter."