Congress will not support lifting the half-century embargo on Castro's Cuba, Sen. Marco Rubio said Wednesday.
"I don't believe they have the voted to lift the embargo; I think they're going to struggle to get the votes to fund an embassy," the Florida Republican said on CNBC's "Squawk Alley."
He later told CNN that he would do everything he could to block any ambassador nominee from even coming up for a vote.
President Barack Obama announced plans Wednesday to re-establish diplomatic relations with Cuba, vowing to expand banking, commerce and telecommunications ties with the country more than 50 years after they were severed.
Obama spoke following a prisoner exchange involving American contractor Alan Gross, who was held in a Cuban prison for five years on espionage charges, and the swap of an American spy held in Cuba for three Cubans jailed in Florida. U.S. officials said Havana also was taking steps to release 53 political prisoners.
"This president has to be the worst negotiator we've ever had in the White House," Rubio said. "In exchange for all that, Cubans are going to agree to release 53 political prisoners who would be right back in jail if they take up the cause of freedom again. ... This is absurd."
Despite the concessions the U.S. has made, Cuba hasn't moved to further human rights and democracy, he said. There will be "no freedom of the press, no freedom of organization, there will be no elections, no democratic opening, nothing. Zero," said the Cuban-American senator, who has been mentioned as a possible GOP presidential candidate for 2016.
He warned it "potentially goes a long way in providing the economic lift that the Castro regime needs to become permanent fixtures in Cuba for generations to come."
Cuban-Americans in Rubio's home state of Florida, including some who fled the Castro regime, have grown increasingly supportive of changes in U.S.-Cuba relations.
"I don't care if the polls say 99 percent of people in Florida want to lift the embargo. I would still be for (keeping) it," Rubio said. "My goal is freedom and democracy in Cuba, and the embargo gives us leverage."
In June, 68 percent of Cuban-Americans favored re-establishing diplomatic relations with Cuba, 69 percent supported lifting travel restrictions, while 52 percent said they wanted the embargo lifted, according to a recent Florida International University poll.
In comparison, 87 percent of Cuban-Americans in Florida supported the embargo in 1991.
"We are witnessing a clear demographic shift with younger and more recently arrived Cubans favoring a change in policy toward the island," said Guillermo J. Grenier, who conducted the survey.
Since 1959, when Fidel Castro's regime took power in Cuba, Miami-Dade County in South Florida has become home to almost 900,000 Cuban exiles and their American-born children, according to the FIU survey.
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—The Associated Press contributed to this report.