Cernig has already hinted at some domestic policy and political consequences of Fidel Castro stepping down, but I would like to extend these thoughts into what a reasonably rational US policy towards Cuba may be if the only objective is not to either dominate the Florida Cuban exile vote, or to keep the margin of loss down to a reasonable number. I don't think either party will want to advocate a reasonable line this election cycle as the GOP needs to consolidate all segments of their base, and the Democrats are running three decent to strong challengers against South Florida Cuban-American Republican Congress-critters. But hopefully we'll change the policy after the election.
Cuba is not a threat, nor should it be an invasion target despite what the Stupidest Man Alive and working at the White House thought. Since the Soviets withdrew their support from the Cuban economy, it has already undergone massive shock therapy and atrophy. It's major export is raw commodities and has little significant value add. It is a bulk importer of basic foodstuffs, some of it American. American farmers are a potential counterweight to the South Florida Cuban lobby as the farmers are looking for new markets. This argument is a bit weaker this year as grain is hitting record prices, but it has been a consistent theme for the past decade.
Cuba is no worse than many countries that the United States routinely deals with, including China. Our domestic soft power package is still an attractive package to many people, and it can be enhanced with tourists enjoying the beaches of Cuba at any location other than Gitmo.
So what does a rational and reasonable US Cuban policy looks like as the previous fifty or one hundred years of policy depending on how snarky one wishes to be have not been successful