Jimmy Carter strides through an impoverished neighborhood of the Dominican town of Dajabon, where cattle mope behind a tangle of barbed wires, where the heat suffocates and the air is thick with mosquitoes.

He marches to a bluff overlooking a river, the sun glinting off his "JC" belt buckle, followed by a pack of barefoot children and their sun-drenched parents. He clutches each hand that comes his way, occasionally dropping a "muchas gracias" laced with his Southern twang.

When he gets to a hovel owned by Juan Taveres, a weathered grandfather whose family was once afflicted by malaria, he eases into a rocking chair. Roosters crow, reporters shuffle, but it seems like they could talk all day, if not for the waiting convoy rumbling up the hill.

"There's no malaria here, right?" Carter asks.

No, Juan responds eagerly.

"And none in the future," Carter declares.

He flashes that smile _ the megawatt grin beloved of editorial cartoonists, an incongruous trademark of a disappointing, one-term presidency.

Nearly three decades have passed since Carter left office. He is 85 years old. Yet here he is, in a torrid, desolate corner of the world pushing two reluctant Caribbean neighbors to fight malaria, a disease that's long been eradicated from richer countries.

And he is smiling, because this is what he does. Since leaving the White House, he's logged millions of miles and visited dozens of countries on missions to wipe out diseases, mediate conflicts, advocate for human rights and monitor elections. He's built a legacy that few, if any, American ex-presidents can match.

"I would say that this life, for the last 25 or 30 years since we left the White House, has been the most enjoyable and the most gratifying," he says.

He'll tell you his motivation stems from a frustrating desire to solve what he believes are solvable problems, from seemingly eternal international conflicts to public health dilemmas. He'll also admit it's driven by his growing sense of mortality, an understanding that his life could end next week or next decade.

But the ex-president's age is also an ally. It gives him "great solace" as he contemplates the inevitable, he says, a feeling of equanimity that helps even out his competitive nature. It's all driving him to make the most of this phase of his life _ even if the grueling pace reminds him of those tiring days of his childhood on the farm.

His wife, Rosalynn, has a simpler explanation.

With a shrug, she says: "He's miserable if he's not doing anything."

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