Marriage isn't just about prohibition. Prohibition implies some activity that can be done in the absence of a governing body. Since you need the government to have your marriage, its not really prohibition when the government says no; hence much trickier. Remember, there was once prohibition against gay people having sex (at least in some states). The law was overturned on the grounds that its too much government, but that argument won't work for marriage licenses. Its still legal to have a gay wedding and list it in the NYT (since thats the private sector doing it).
As for pot, our last three Presidents (counting Obama) admited to smoking it. The last two were also known to do more than just pot. If you think any of these hipporities will legalize pot anytime soon, you must be on something yourself. Remember, NEVER trust a former pot head to legalize pot. If you want pot or prostution to be legal, its best to vote for someone who never did it, and is otherwise sqeaky clean.
As for travel to Cuba. Well, Cuba is a former communist country turned socialist. Obama is a socialist. So there you go. Restrictions on travel to Cuba have some chance of getting lifted ;-p.