Ron Paul is a neo-isolationist, not a Nazi. He appears to be antisemitic because his wacko foreign policy works to the disadvantage of Israel. But he has the utmost respect for several important (since deceased) Jewish intellectuals of the past in the libertarian movement, some of whom he had personal contact with - Ayn Rand, Murray Rothbard, Milton Friedman, Ludwig von Mises, Friedrich Hayek - and who influenced his economic views.
One can be isolationist without being anti-Israel. Paul is anti-Israel. He has made his distaste for that country plain on numerous occasions.
This anti-Israel philosophy doesn't so much come from isolationism or libertarianism, but European style rightism, which is abundant among "palaeoconservatives," whether libertarian or statist.