KAYONZA, Rwanda — Bill Clinton could not stop talking about soybeans. Over dinner in Kigali with a handful of longtime political aides and deep-pocketed donors, he recited the price of soy (“It never exceeded $8, and now it’s $16”) and extolled its virtues as a miracle crop (“You can grow it with just a thin layer of topsoil”).

The following day, he and his daughter, Chelsea, took a tour of a future soybean processing plant here, still a red-dirt construction site at the foot of misty green hills. Mr. Clinton swatted a fly out of his eye and predicted that demand would soar. “The Chinese can’t drink milk, so they rely on soy,” he said.

But when the manager at the plant asked him to return next year, when production will provide work to as many as 1,400 farmers, Mr. Clinton turned the subject to himself.

“I’m older than you,” he replied. “We have to be sure I’m still around.”

In conversations, Mr. Clinton frequently gives the sense that he feels as though he is living on borrowed time. And the world that he now inhabits — the global philanthropist on a journey to cure the world’s ills and burnish his legacy — is far from the muddy terrain of partisan politics that he will return to on Wednesday night at the Democratic National Convention.