Today? How about we just start with the guys with the swastika tattoos and fasces flags chanting 'Jews will not replace us!' they certainly call themselves that. 
What makes them different : they declared themselves different. It's the cornerstone of their ideology.  If you think other people are lesser and do not respect their right to live they have no obligation to respect yours. 

Then: read a history book.
There is no difference in the doctrine. Only the advertising has changed,and not even much. Alt-right is just Nazi rebranded to make recruitment easier. They don't even do it for long. Soon as you're in they bring out the old branding again. 

It's not an ideology that gets to be tolerated or allowed to exist unchallenged.  This is a settled matter. We literally had a war over it. The entire world was involved.