Critics argue that Mr. Obama's opening to Cuba is ill-timed for that very reason: Instead of easing trade barriers against the island, they say, the U.S. should be doubling down on economic pressure against the Castro regime at a time when it is most vulnerable. But the Cuban regime has proved remarkably durable. Moreover, we've established normal diplomatic and trade ties to other former enemies such as China and Vietnam — with whom, unlike Cuba, we've actually fought long and bloody wars. Those countries are hardly liberal democracies today, yet we no longer treat them like pariah states. Why should Cuba, which poses virtually no serious national security threat to the U.S., be any different?