Just an update that my friend - dual French/US just went to/from Cuba from the USA (on a US passport) without incident. On her return to the US, immigration apparently only asked if she enjoyed her trip and didn't ask any questions regarding the reason for her visit. Obviously they have 5 years to audit her; but it appears to me that "support the Cuban people" as long as reasonably documented is currently fine. BTW all her US friends that she went with received the same treatment.