It goes like this: "We need guns so that we can resist the government when it becomes tyrannical. And when does the government become tyrannical? When it comes to take our guns away."
Circular reasoning (also known as paradoxical thinking or circular logic), is a logical fallacy in which "the reasoner begins with what he or she is trying to end up with". The individual components of a circular argument will sometimes be logically valid because if the premises are true, the conclusion must be true, and will not lack relevance. Circular logic cannot prove a conclusion because, if the conclusion is doubted, the premise which leads to it will also be doubted. Begging the question is a form of circular reasoning.
Emphasis mine.