Oh I'll tell you exactly where this comes from. This picture and what it represents.
This is a photo of refugees from Syria and Iraq entering Austria, en-masse, last year. We've all read about the refugee crisis in Europe. These human flows have happened, but they are spurned by:
-> There is a large land connection from a massive war zone, to continental Europe
-> Russia and Syria have weaponized the refugee crisis to put pressure on the EU and Europe as part of their foreign policy.
It however, represent something basic to the alt right, a huge swarm of brown people flooding into lands occupied by white people. But it also represents something else: not something that is happening in America.
The Alt-Right is intrinsically racist. They dress it up in words and stunts, but at the basis of their entire belief system is the fact that White Americans are rapidly going from being a majority in this country to a plurality, to eventually minority-majority. The alt-right is the pushback. But the one thing they don't have is what you see above: waves of brown skinned people flowing into our borders. Mexicans and Central Americans are simply not doing that.
But their entire world view requires it.... so they've engineered the idea of it. They keep repeating the same lies about illegal immigration, to create the idea that this wall is needed. This wall is just a monument to their xenophobia. It is a symbolic declaration of intent, not a functional thing: Brown people stay out.
Basically, they're making their own reality, because they want to be racist.