The Man Nobody Knows.(Nestor Kirchner)

When a little-known provincial governor named Nestor Kirchner first declared himself a candidate for president of Argentina, his wife, Cristina, reacted with three words: "You are crazy!" She was not alone: the opinion surveys gave the 53-year-old Peronist less than 10 percent of the vote throughout most of last year, and as recently as six months ago the notion of a President Kirchner seemed about as far-fetched as a Buenos Aires steakhouse running out of red meat. But when 25 million Argentines go to the polls in next Sunday's presidential runoff election, the low-key Kirchner is expected to trounce his own party's longtime leader, former president Carlos Menem. If that happens, the vast majority of Argentines will be making a leap of faith: a headline in a recent issue of Argentina's leading newsmagazine christened Kirchner "The Candidate Nobody Knows."

Actually, Kirchner is not a complete political stranger. A product of the Peronist party's "progressive" wing, he railed throughout the campaign against the corruption and free-market economic policies that stamped Menem's 10-year presidency. That message struck a chord; most Argentines trace the roots of their country's worst-ever economic crisis to the waning months of Menem's second term in the late 1990s, when government spending jumped sharply and a deep recession took hold. Kirchner's projected victory, then, would have less to do with his own popularity than with the voters' resolve to punish Menem for the mess he left behind.

A proponent of neo-Keynesian economics, Kirchner has invoked some of the Peronist party's old populist rhetoric. He advocates a greater role for the state in putting Argentina back on the road to recovery. It was no accident that Kirchner, bolstered by a new poll that gave him a 37 percentage-point lead over Menem, flew to Brazil and Chile last week for meetings with the center-left presidents who run those countries. "Kirchner is a 1970s-style Peronist," says economist Norberto Sosa. "He's a defender of national interests, and he sees Menem as having betrayed the party's traditional values."

Kirchner's ascent, in large measure, has to do with a bitter vendetta between Menem and outgoing care-taker President Eduardo Duhalde, who took office early last year at the nadir of Argentina's economic meltdown. Duhalde had a falling out with Menem during the 1990s, and he scoured the Peronist party's top ranks for a politician who could turn back Menem's bid for a third term. When Duhalde's first choice declined the invitation and another ally fizzled in the polls, he settled on Kirchner almost by default. A descendant of Swiss and German immigrants, Kirchner had compiled a respectable record in his 11 years as governor of Santa Cruz province--a remote, oil-rich region of only 200,000 people that occupies the southernmost tip of the continent--but to most Argentines he was "Nestor Who?"

The relationship involves tradeoffs. Duhalde assigned two of his key aides to help run the Kirchner campaign, and he prevailed on the candidate to retain Economy ...