Colombia stands out as an oasis of conservatism amid Latin America's growing legion of leftist leaders and Sunday's elections are unlikely to change that with President Alvaro Uribe expected to win by a landslide.

But a last-minute surge by a leftist candidate nicknamed "Santa Claus" has provided the lone surprise in a campaign dominated by Uribe, Washington's staunchest ally in the region.

CountryWatch: Colombia

Colombia's democratic left, long blemished by its association with the four-decade-old guerrilla insurgency, has been invigorated by the surprise performance of Sen. Carlos Gaviria, the candidate for the Alternative Democratic Pole party, or PDA.

Unknown to half of Colombians just a few months ago, the academic and former head of Colombia's highest court has leapfrogged past Liberal Party candidate Horacio Serpa to move into second place. Since March, polls show that support for Gaviria has tripled to 24 percent.

Meanwhile, Uribe, popular for his crackdown on leftist rebels and armed groups, has seen his still commanding lead dip 10 points to 55 percent.

"He's run a very effective campaign, which is why he's the only candidate to see his numbers improve during the course of the campaign," said pollster Napoleon Franco.

Call it the Santa Claus effect.

Colombians affectionately refer to the 69-year old political newcomer as "Papa Noel," or Santa Claus, as much for his cuddlesome paunch and hoary beard as for his mild-mannered campaign style and high-minded discourse.

More at ease writing poetry than kissing babies, Gaviria looks nothing like the populist firebrands voters in Venezuela and Bolivia have ushered into power in recent years.

"I want to show Colombians that being a leftist doesn't mean you have to be aggressive," Gaviria told The Associated Press in a recent interview.

But looks can be deceiving. Gaviria's opposition to a free-trade pact with the United States and harsh criticism of the free market firmly aligns him with the region's other leftists. So does the poster of Cuban president Fidel Castro and Che Guevara that hangs prominently in his campaign headquarters.

As Uribe's support has slipped dangerously close to the 50 percent threshold needed to avoid a second-round runoff with his closest rival, the president has intensified his attacks against Gaviria, urging voters to stay clear of "disguised communists."

In response, Gaviria has accused his former student of employing McCarthy-like fear tactics, an allusion to U.S. Sen. Joseph McCarthy's anti-communist witch hunt in the 1950s.

"Uribe's biggest defect is his authoritarian streak, which makes him intolerant of criticism," said Gaviria, who was Uribe's law professor at the University of Antioquia in Medellin.

About Uribe's academic career, Gaviria jokes: "He was a good student, but he forgot to come to the class on constitutional law."

Key to Gaviria's popularity is his background as magistrate of Colombia's constitutional court — an institution esteemed like few others in Colombia as beyond the pale of corruptible politics. As head of the court from 1996-2001, Gaviria ruled in favor of everything from same-sex civil unions to the decriminalization of small doses of drugs — progressive views that Uribe has seized on to shore up support among his conservative base.

Equally important has been the collapse of what has been for more than a century Colombia's largest electoral machine: the centrist Liberal Party. Despite a small slip in support for Uribe, Gaviria has stolen the bulk of his votes from third-time candidate Serpa, who is running third with 10 percent. He lost to Uribe in 2002 with 32 percent of the vote.

A second-place finish for Gaviria could tank the ideologically rudderless Liberal Party once and for all. But more importantly, it could set the stage for the PDA's emergence from the political fringe into a modern, mainstream party, like Brazil's ruling Workers Party.

"The most the left has ever won in a presidential election is 680,000 votes and we're hoping to get 3 million," said Gaviria.

To effectively compete for power in 2010, a lot depends on what kind of opposition Gaviria and his party play over the next four years. With only 11 of 102 legislators in the incoming Senate, their ability to affect legislation will be slim.

Moreover, the PDA is an umbrella group that includes a diverse range of constituencies from former guerrillas and communist labor leaders to centrist middle-class voters and social democrats.

"Gaviria is keenly aware that his mission in this race is to unify his own party," said Rodolfo Arango, a close friend and philosophy professor at Bogota's Andes University.