Barack Obama has made a geopolitical irrelevancy suddenly relevant to American presidential politics. For decades, Cuba has been instructive as a museum of two stark failures: socialism and the U.S. embargo.

Now, Cuba has become useful as a clarifier of different Republican flavors of foreign-policy thinking. The permanent embargo was imposed in 1962 in the hope of achieving, among other things, regime change. Well.

Fidel Castro, 88, has not been seen in public since January and may be even more mentally diminished than anyone — including his 83-year-old brother — who still adheres to Marxism.