This article from the New York Times is really a must read.  It does a good job of parsing out exactly what these emails mean:
Stephen Miller’s Sinister Syllabus
Leaked emails from 2015 and 2016 show one of Trump’s top advisers trying to teach Breitbart editors a thing or two about white nationalism.
To quote from part of it:

But suspecting Miller’s ideological allegiances is quite different than knowing them. In the absence of proof, there was room for plausible deniability. That’s how a conservative magazine editor could praise Miller as a “wunderkind” for his command of the “details” of immigration policy while dismissing evidence that Miller was once close to Richard Spencer, a prominent neo-Nazi.
With the emails — supplied by Katie McHugh, a former editor at Breitbart — we now know what Miller was reading and thinking about in the year before he joined the Trump campaign. And there’s no denying the nature of the material.

Also worth watching:
Does Stephen Miller Remain In The White House? | Morning Joe | MSNBC 



All of this is just further confirmation, if any were needed, that I was not too harsh last month when I wrote that there can no longer be any doubt that this is a fascist Presidency.