IMHO the Cuban Embargo was an unconstitutional usurpation of power by the Federal Government.
Think about it: Telling US citizens that they can't go to some place the government doesn't like because they're forbidden to spend US currency there (or spend other "hard" currency they bought with US currency), and going there requires spending money? Shades of the Iron Curtain and Catch-22. (If the US government wants to forbid such a thing and have even a chance of finding a Constitutional authorization, they need to DECLARE WAR against Cuba - and then actively fight it.)
If a law is unconstitutional, it doesn't exist, and hasn't from the moment of its passage. Why should The Donald obey a non-law?
But even if you don't believe the law is unconstitutional: The hypocrisy of anti-trump forces zinging him for dealing with Castro just floors me. These are the people who have made - and still make - heroes and heroines of Castro, Che Guevara, Bill Ayers, Angela Davis, and "Hanoi Jane'" Fonda, and a virtue of "Civil Disobedience" to laws they don't think are right, politically correct, or convenient. Do they REALLY think Trump's supporters would be swayed by this argument from THEM? B-)