The Illegality of what you're doing really is a non issue now. Here's the situation...
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Hundreds and hundreds upon thousands of American tourists have travelled to Cuba illegally. The most common gateway is Canada and Mexico. Here's a thumbnail sketch of the situation...
1.) First of all, Americans are welcomed with open arms in Cuba and they always have been. The problem has always been with the US government, not the Cuban government.
2.) The only way to legally visit Cuba from the US is under license from the US Treasury Department and tourist travel is NOT licensable under ANY circumstances. There are no loopholes or exceptions. The, "not illegal to travel there, it's only illegal to spend money" is an urban myth. There is no way for an American tourist to be fully hosted or for an American tourist to purchase an all-inclusive package outside of Cuba so they're not spending any money there.
Bottom line: It is illegal for any American citizen - and in fact for anyone even residing in the US no matter what their citizenship - to visit Cuba as a tourist. You're breaking the law, period.
3.) To get around the travel restriction American tourists visiting Cuba illegally must fly there via a third country. Direct non-stop gateways to Cuba from the Western Hemisphere include Canada, Mexico, Bahamas, Costa Rica, Dominican Republic, Grand Cayman, Guatemala, Nicaragua, Panama, Venezuela and wherever else I'm forgetting. There's a myriad of other choices that transit through Panama, etc.
In other words, compared to many other Caribbean island destinations Cuba is a very easy destination to reach...
4.) The US Congress has dried up funding for prosecution of illegal tourist travel so the OFAC (Office of Foreign Assets Control) ceased all active investigations regarding tourist travel several years ago.
5.) Let's consider the worst case scenario... Imagine you completely lose your mind and upon returning home admit to US CBP (Customs and Border Protection) that you visited Cuba or that you were stupid enough to somehow give US CBP irrefutable proof that you went to Cuba. What would happen?... You'd negotiate a settlement of $250 - $1,000 with the OFAC, pay the fine and forget about the entire episode. No trial. No prosecution. No criminal record. NOTHING.
6.) There hasn't been one single OFAC legal investigation in history initiated by or supported by passenger manifests. I won't go into a detailed legal explanation here but this is a non-issue and completely immaterial for any American visiting Cuba as a tourist.
Any American tourist planning to visit Cuba obviously needs to do their own research and figure this out for themselves. There's a multitude of resources on the Internet that address this insane legislation so it's simple for anyone to educate themselves and know all the facts before they knowingly break the law.
I applaud all the Americans who travel to Cuba in spite of the ridiculous US Embargo. More power to them for ignoring this embarrassing and immoral piece of US foreign policy.
Cheers,
Terry