I have some serious issues with a number of the statements in the article in the original post. In particular, equating the number of members of the KKK (not even including the LWK) with the number of white nationalists in this country is absurd, the number of "members" of the altright cannot be determined by the number of people who have registered accounts on /r/altright, and stormfront had 300,000 members at peak within the last few years. That's just off the top of my head. It's also worth noting that there was an 18% increase in the number of KKK chapters in this country in the last year.
Furthermore, a graph depicting the prevalence of strong racist tendencies that ends in the late 90s and somehow believes it "presumably remains" in that level today is ridiculous. That's 20 years ago, for those counting, and the number of hate groups and white nationalist/separatist groups and group members changed significantly under President Obama. And not for the better. Those graphs also tell a story that is very important right now. If they even stayed at the 1999 levels, we're talking about roughly 4-5% of the population would not vote for a black candidate of his/her party if qualified. That sounds like a really small number, until you consider that there are about 218MM registered voters in this country. That's roughly eleven million people holding that view. Which, compared to 1996 numbers, would be an increase of around a million people, despite static percentages. It is unlikely that those people voted for Clinton. Consider as well the links inside that article - by 2012 the number was 4% according to the same polling (but not included on graph.) 2016, that number was 7%. It nearly doubled in four years leading up to this election. And again, if those numbers are correct you're talking about over fifteen million people.
That said, true, members of identifiable hate groups do not make up the majority of Trump's supporters. But they make up a very vocal segment, and they're being used intentionally by the administration (particularly, in my opinion, Bannon) with full knowledge of what makes those groups tick. I do not believe that Trump is a "true believer" in any way. I don't believe Stephen Bannon is, either. But they are using racial animus (and religious, and orientation, and misogyny) in order to create a new coalition in the manner of Nixon's, only more reactionary and, in many ways, more intellectually capable and focused. The alt right began as a group of free speech ideologues who expressed that freedom through statements considered unacceptable to polite society, which made it a haven for white nationalists, neo nazis, and other bigoted organizations, to the point where they have strong control over the movement behind Richard Spencer of the National Policy Institute.
Anyone claiming Trump is Hitler is reaching. Anyone who isn't at all concerned about Bannon or the alt right movement is missing what's going on.