On Wednesday morning, senior American officials told reporters about the release of Alan Gross, an American USAID subcontractor who had been held in prison for just over five years in Cuba.

Gross, whose detainment inspired a passionate and high-profile public campaign for his release in the United States, has reportedly been swapped for three members of the "Cuban Five"—five Cuban spies who were arrested in Miami in the late 1990s and later convicted on espionage and conspiracy charges. The imprisonment of the Cuban Five, who are widely considered to be heroes in their home country, has also produced a high-profile release initiative in Cuba. (Two of the five were released over the last few years.)

This sudden development immediately roused speculation that the long-standing U.S. embargo against Cuba might finally be on its way out.

That talk, however, may be premature. Overturning the embargo requires, among many things, congressional legislation and approval, which as history proves can be extraordinarily thorny. As Peter Baker notes, the deal struck to release Gross, which Cuba claims was done on "humanitarian grounds," has already engendered criticism, even from within the president's own party. Senator Robert Menendez, a Democrat and the Foreign Relations Committee chair, offered this rebuke:

Let’s be clear, this was not a ‘humanitarian’ act by the Castro regime. It was a swap of convicted spies for an innocent American. President Obama’s actions have vindicated the brutal behavior of the Cuban government.

Menendez's statement was echoed by Senator Marco Rubio, who said that the agreement would give the Castro regime a needed "economic lift."