I have no opinion on whether or not Rand Paul is an anti-Semite. However, this resonates strongly with me:
But. The Achilles heel of libertarianism has always been foreign policy. Libertarians–Ron Paul is a good example–tend to justify their isolationism by arguing that U.S. foreign policy explains, maybe even justifies, hostility toward us, and if we would just keep to ourselves, there would be no need for a strong defense. A particularly ugly elaboration on this theme holds that America’s problems in the world stem largely from our alliance with Israel, and if we would merely cut the Israelis loose, all would be well in the Middle East, and perhaps elsewhere. Ron Paul, while by no means the most extreme instance, tended in this direction.
Sorry, libertarians, but we can't just stick our heads in the sand. Like it or not, the world has more than just the US in it, and we can't simply opt out.