I don't think the GOP/NDP comparison is apt, because Germany attempted to ban the NDP completely and the NDP works continuously with literal Nazis. If the KKK had a political party of its own, that would be comparable. There are only a few thousand members of the KKK left, though, so that is unlikely to occur.

I think that for the same percentage to identify with Nazi ideology it would require millions of people to be so comfortable with it that they would openly give Nazi affiliated parties their support.

I don't think millions of people support Neo-Nazis in the US.