(CNN) -- When an opposition candidate challenged Venezuelan President Hugo Chavez to a debate last month, his reply was "aguila no caza mosca" -- "the eagle doesn't hunt the fly."
The challenge came from presidential candidate Maria Corina Machado. Machado chose a momentous occasion to challenge Chavez: his yearly address to the Venezuelan National Assembly (of which she is a member), an event broadcast live on national television.
"Time has run out," Machado said in front of an audience of shocked members of the assembly. "It's time for a new Venezuela. You should accept to debate, Mr. President."
In replying, Chavez suggested that Machado should first win the primaries. "That's what you should do. You're not really at my level to debate with me," Chavez calmly said.
For Chavez, who has been in power for 13 years, dismissing the opposition as weak is part of his political strategy. His favorite term for his opponents is "escualidos," which in Spanish means not only filthy and neglected, but also feeble.
With a combination of populist programs and a centralized control of his socialist agenda, the power equation in Venezuela has remained the same for much of Chavez's time in office. But that equation might be changing.
In the past few weeks, Henrique Capriles Radonski, the 39-year-old governor from Miranda state, has taken Venezuela's political scene by storm. Polls show Capriles is the only candidate with a real chance of beating Chavez in this year's presidential elections, to be held on October 7.
He is widely expected to win this Sunday's opposition primaries and form a coalition against the incumbent.
Capriles has sought to unify the opposition and to appeal to different constituencies. At a recent political rally, he said, "This is not the hour of the left or the right. This is Venezuela's hour."
The founding member of the Justice First Party defines himself as a center-left candidate, favoring policies similar to those of Brazil's former president, Luiz Inacio Lula da Silva. Lula's political platform in Brazil was promoting capitalism-friendly initiatives while at the same time spearheading social programs for the poor.
Capriles, a former tax attorney, was the mayor of Baruta, a Caracas suburb, before winning the governorship of Miranda, which adjoins the Venezuelan capital. He was also the youngest vice president of the now defunct Venezuelan Congress.
His campaign slogan is "There is a Way" and he constantly invites people to get on the "Bus of Progress."
Part of his appeal is that he speaks about "solid government institutions" and a judicial branch that treats "all Venezuelans equally under the law." Chavez has been accused of being fiercely loyal toward his supporters and promoting patronage at the expense of his political enemies and the rest of the country.
Last month, Capriles, whose grandparents were Polish Holocaust survivors, forged an alliance with Leopoldo Lopez, a major opposition candidate. Lopez, from the Popular Will party, hugged Capriles at a rally attended by supporters of both men.
"I tell you, Henrique, my brother, you will be the next president of Venezuela," an energetic Lopez said. This alliance gave Capriles a boost in his approval rating, currently at 56 percent.
Capriles stepped onto the national scene during a 2002 riot at the Cuban Embassy in Caracas. The Chavez government accused him of inciting the riot and sent him to jail for four months, but the courts ended up acquitting him.
Besides Capriles and Machado, Zulia state Gov. Pablo Perez, economist and diplomat Diego Arria, and labor leader Pablo Medina are also running as opposition presidential candidates. But polls show their approval rating is well below that of Capriles.
Journalist Osmary Hernandez in Caracas contributed to this report.