UPDATE: Oh, this is as good a place to mention something I'd meant to write before. The notion that our embargo or blockade or isolation of Cuba hasn't worked ignores that Cuba is not suffering from an embargo, blockade, or isolation from the rest of the world:
Normalization has not advanced democracy in China or Vietnam. Indeed, it hasn’t done so in Cuba. Except for the United States, Cuba has had normal relations with the rest of the world for decades. Tourists, trade, investment from Canada, France, Britain, Spain, everywhere. An avalanche of nylons — and not an inch of movement in Cuba toward freedom.
So we didn't have 50 years of a policy of isolation.
Indeed, it would be more accurate to say that 50 years of Cuban isolation of America has pushed our system closer to Cuba's socialism.