The U.S. State Department’s lead negotiator with Cuba said at a hearing today that she has “no illusions” that the Castro regime will change after the two nations announced normalized relations with each other.

In the first of three congressional hearings this week on President Obama’s new Cuba policy, Roberta S. Jacobson, the assistant secretary of state for Western Hemisphere affairs, took heated questions from a subcommittee led by Cuban-American Sen. Marco Rubio, R-Fla.

Jacobson, who recently headed a U.S. delegation that traveled to Havana to discuss the restoration of diplomatic relations, argued that Obama’s policy is about “empowering” the Cuban people to pursue a free and democratic life in the face of a regime that she admits is unlikely to change.

“I am absolutely confident that Cuban people will prevail and will be empowered to prevail under this new policy,” Jacobson said. “This policy is not based on the Castro regime changing. We have no illusions over that. It’s about empowering the Cuban people.”

“This policy is about empowering the Cuban people,” says Roberta Jacobson of @StateDepart.

Rubio, the most outspoken congressional voice against Obama’s Cuba policy, used the occasion to unload on the move.

Calling Obama’s policy “disgraceful,” Rubio, a likely Republican candidate for president in 2016, said:

“It’s no secret that I have deep reservations, and in many instances, direct opposition, to many of changes for the simple reason that I feel they won’t be effective in achieving the political opening we all desire for the Cuban people.”

As Rubio and others, such as Sen. Bob Menendez, D-N.J., continued their assault on the new policy, Jacobson and her counterpart at the State Department, Tomasz Malinowski, stayed steadfast in support of the policy shift toward Cuba.

But they acknowledged the Castro regime has continued its brutal behavior since Obama announced the new policy on Dec. 17.

Malinowski, the assistant secretary for democracy, human rights and labor, said the Cuban government detained 140 political prisoners in January.

“The nature of the Cuban regime has not changed and we have not claimed so,” Malinowski said.

Added Jacobson, of the new U.S.-Cuba relationship: “We have shared interests, but sharp differences. This administration is under no illusions about the nature of the Cuban government.”