The USA and Cuba
The US government has embargoed Cuba since 1960, and it's been less than an enormous success. Castro is still in office and while he is your standard journo-imprisoning dictator, he still seems popular and will be hard to shift.
The reasons why the blockade (el bloqueo) is still in place has little to do with Castro. Experience with nominally Communist regimes show that they can be overwhelmed by a tsunami of cash if opened to world trade. It may be so that the charming boulevardes of Havana would be uglified by fast food logos, but that's up to those who live there rather than a government in an ongoing snit that it can't engineer a junta.
El bloqueo is still in place because Cuban emigres have become politically and economically successful in Florida, a key state in US elections. Those emigres control trade networks to (and largely within) Cuba, so that Cubans have to be connected to them in order to get the meagre offerings they offer (and a well-connected Cuban can get access to pretty much anything, as much as any well-connected person in any country). Lifting the blockade would cut out these middlemen. Pre-Castro Batista used to be in cahoots with the Mafia, now present-day Cuba is all but owned by a Miami Mafia who ply their trade out of sight, out of mind of the US Justice Department.
If Florida went Republican and the rest of the US went Democrat, you might see some movement on this policy. Castro would claim it as a victory, but would dither and grumble about preserving his socialist dreams and shake his spotty old fist at overwhelming twentyfirst century consumerism like everyone else his age. If Fidel Castro died, his brother Raul would be unable to get the support necessary to hold it together.
Alternatively, who knows what W might to in his last two years? Nah, not with his brother as Governor, and the Dems might claim credit after he copped the grief from the right. You'd probably need a Democrat who lost Florida to do this, or a Republican with some guts like McCain. You may even need a Hispanic President. Alternatively, you could piss about for another 46 years.