On a December afternoon nearly 50 years ago, I got a phone call from Jody Powell, the press secretary to a little-known former governor of Georgia who had this bizarre notion he would be the country’s next president.

After filling me in on his boss's plans for formally announcing his candidacy the next day, he asked if I'd like to speak to “Jimmy.” Sure, I said, and he connected me with the soft-spoken Southerner whose presidential aspirations I'd been watching with skepticism and some amusement.

Then, Jimmy Carter explained to me, as he did to other doubters in the press and elsewhere, how he planned to get elected.

Often since, I've thought about that phone conversation with Carter and Powell, holed up in a nondescript Holiday Inn near the U.S. Capitol, seeking to persuade political writers like me to take his candidacy seriously.

As it turned out, Carter’s rise from the hamlet of Plains, Ga. (pop. 683) to the White House was the most remarkable political story I ever covered — at least until Donald Trump’s election. And the man whose 100th birthday we mark next week — three years after he and wife Rosalynn celebrated their 75th wedding anniversary — was probably the most unusual to win the presidency in the 20th century.

A graduate of the U.S. Naval Academy who became a nuclear engineer, he left service to revitalize his family's rural Georgia peanut farm after his father died.

Though his 1970 gubernatorial campaign was hardly high-minded, once elected he helped erase vestiges of the state’s segregationist past. As president, he helped launch the long process of bringing peace to the Middle East, an effort most of his successors have pursued, unfortunately with only mixed success.

During his lengthy post-presidential years, he has written more than 30 bestselling books — his main source of income. A voice for human rights around the world, he has been a prod to succeeding presidents, both Democrats and Republicans.

Despite being afflicted with various forms of cancer, his family’s scourge, he long ago became the nation’s longest-lived president, still politically aware and hoping — son Chip said recently — to cast a ballot next month for another trailblazer, Vice President Kamala Harris.

Though highly intelligent, he was often politically tone deaf, seemingly believing that, since good would inevitably triumph over evil, political compromise was unnecessary. Often rigid, moralistic and humorless, he was as likely to glare at his most loyal aides as to praise them.

He correctly foresaw the Democratic Party needed to recapture the political center. But in the process, he sharpened the internal split with its liberals that contributed to his landslide reelection defeat in 1980.

He sought to strengthen the military and balance the budget. But he failed to cope with an oil shock sending inflation soaring and the 444-day detention of 60 U.S. diplomats by militants who had ousted Iran’s longtime pro-American leader, Shah Mohammad Reza Pahlavi.

Unexpected events and a lot of luck helped Carter become the only Democrat to win the presidency between the 1960s and the 1990s.

Richard Nixon’s resignation in the face of almost certain impeachment and conviction opened the way for an inexperienced moralist who wasn’t a tricky politician and promised not to lie to the American people.

And George McGovern’s disastrous 1972 defeat prompted Democrats to back a moderate Southerner who could bury the party’s segregationist legacy.

His Democratic opponents helped.

When Washington Sen. Henry Jackson, backed by defense hard-liners, and Alabama Gov. George Wallace passed up the New Hampshire primary, Carter occupied the center-right and, with just 28%, defeated his more liberal rivals.

Then, when the leading liberal hopefuls bypassed Florida, he ran to the left and defeated Wallace and Jackson. Along with his earlier success in the hitherto insignificant Iowa caucuses, those victories provided the political momentum to win the nomination, despite continued enmity from the party’s establishment and a series of too-late primary challenges.

That fall, President Gerald Ford inadvertently gave Carter a crucial boost. Already weakened by his pardon of Nixon and Ronald Reagan’s conservative challenge, Ford inexplicably declared in a nationally televised debate that Communist-controlled Poland was free — and repeated it several subsequent times.

In a political fluke akin to Trump’s 2016 victory, Carter narrowly won. He restored (for one election) the Democrats’ former Southern primacy and won Ohio by 11,000 votes and Hawaii by 7,000. Clinching the contest by carrying Mississippi at about 3:30 a.m. the next morning, he headed back from Atlanta to Plains.

Even in victory, however, Carter had difficulty being gracious. When a press bus took a wrong turn going to the airport, he sought to leave without them until aides dissuaded him.

But the delay enabled him to arrive in his little hometown as the sun rose and the morning television shows came on the air.

“I told you I didn't intend to lose,” he told the hundreds who had waited all night around the old train station that served as his headquarters.

“I came all the way through, through 22 months, and I didn't get choked up until” — his voice broke, and he paused, too overcome with emotion to continue, dabbing a tear from his left eye before he willed himself to finish — “until I turned the corner and saw you standing here.”

There were few dry eyes. It was a scene none of us ever forgot.

Carl P. Leubsdorf is the former Washington bureau chief of the Dallas Morning News.