The Trump administration has banned American cruise ships from Cuba from June 5 2019, and removed the option for what is known as ‘people to people’ travel for groups and individuals visiting Cuba.
Americans, and those subject to US jurisdiction (eg UK travellers boarding an AA flight from Miami to Havana) continues to be legal under the several US Treasury permitted categories of travel. This includes the much favoured ‘Support for the Cuban people category’. More details here: