Part os the reason is what Harrybaracyda said , but big part is the composition of the country and it's geographical location.
As immigration from Europe decreased and immigration from other part of the world increased the original European settlers saw a distinct change in the demographics ,
After WW2 most of the economic system of the world was destroyed, and the US took the slack , creating unparalleled wealth in the US and the mistaken impression by those European early settlers, that it was because they were superior people.
As the rest of the world developed and started claiming their part of the pie, consequently the US part of the pie began to shrink ,
Those early European settlers who mistakenly thought their success was due tp their superiority as human beings also mistakenly attributed their decline to the new immigrants, where it was actually the new immigrants and the brain drain from their country and into the US that had slowed down the decline.
The mostly whites of European decent protesters in Virginia shouted "you shall not replace us" and degenerate in what they thought was clever "jews shalt not replace us"
trump promised them to "Make America Great Again" , Again? what past period was he going to recreate again? was he going to carpet bomb Japan, and Europe, and send China back to the stone age?
Just like Brexit in the UK, trump promised to take them back to a place that does longer not exist. The only way possible is forward, and from the look of the protesters, replacing them would be the best thing that could possibly happen to the USA.