As may have been the case in Iran, Mr. Trump’s focus on Cuba appears to be driven by the perceived ease of the Venezuela operation, in which the capture of Mr. Maduro led to the quick emergence of a more accommodating partner, Delcy Rodríguez. But the president seems to lack a clear vision for a Cuba intervention: He has recently floated options including a friendly takeover, a “liberation” or, according to recent reporting, economic liberalization without full regime change.