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.


In a speaking slot typically reserved for the vice president, Mr. Clinton will place Mr. Obama’s name into nomination. The invitation serves as a reminder of how far Mr. Clinton has come in four years to refurbish his image and restore his frayed relationship with the Democratic Party after Mr. Obama defeated his wife in the 2008 presidential primary campaign. And it shows how much Mr. Obama has come to rely on a predecessor he once criticized to serve as both role model and validator.


For many Democrats, Mr. Clinton’s renewed stature and his appeal to rural and white working-class voters, a vital group that Mr. Obama has struggled to connect with, make him both an ally of the current administration and a constant reminder of its political shortcomings.


“The excitement of ‘hope’ and ‘change’ aren’t what they used to be,” said Hank Sheinkopf, a Democratic political consultant who worked for Mr. Clinton. “Bill Clinton represents the America Barack Obama needs to get back.”


At 66, he has outlived most of the men on both sides of his family. The man who was known to jog to McDonald’s, and who underwent quadruple bypass surgery in 2004, no longer eats meat or dairy products, and his skinny frame looks almost frail and unnatural carrying his outsize personality.


Confronting, perhaps, the prospect of a future without Bill Clinton, he is bringing his family deeper into the William J. Clinton Foundation, the charitable organization that he started in 2001. His wife, Secretary of State Hillary Rodham Clinton, has said she will return to charitable work after President Obama’s first term, and his daughter has taken on a more active role in recent years. “I told her, ‘Chelsea, you’ve got to suck it up if you want to have a life with a public impact,’ ” Mr. Clinton said.


A Breakneck Tour


The visit here to the soy plant, partly financed by his foundation, was part of Mr. Clinton’s six-day tour in July to South Africa, Mozambique, Rwanda and Uganda. The roadshow gave Mr. Clinton, his daughter and a group of donors and aides who have been allied with the Clintons since their Arkansas and White House years a firsthand look at the philanthropic work that has consumed most of his post-presidential energy.


The trip had the singular feel of a Clinton campaign tour, with a breakneck schedule of speeches and meet-and-greets, Secret Service agents, a chartered Sun Country 737 and lots of Arkansas wisdom. (“We have a saying in Arkansas: If you find a turtle on a fence post, he didn’t get there by accident,” Mr. Clinton told a group of bewildered nurses in Kigali.)