Why was Cuba thought to be a threat in the early 1960s?

It was communist and given weapons by the Soviet Union that could reach U.S. soil.
It was democratic and had set up a naval blockade to stop trade with the United States.
It was close to U.S. soil and built missile bases from materials made in the United States.
It was ruled by the Soviet Union and was trying to prevent the U.S. democratic elections.