This is a rare moment to put the old grievances to one side and build a bridge to the Cuban people.
President Obama's decision to open up a dialogue and re-establish diplomatic relations was a step in that direction.
But now diplomacy-by-tweet is about to take over. Donald Trump is raising doubts about the entire framework of a new future for US-Cuban relations.
It will infuriate the current Obama Administration and make European governments despair over how future US decision-making will be made.
Terminate the deal? And do what?
The embargo is still in place, so we have to assume that he will end diplomatic relations and reignite the Cold War enmity that gave the island the symbolic significance it enjoyed for 50 years.