Leaked emails from Stephen Miller reveal an obsession with white nationalism, the Confederacy and the denigration of minority communities.
"This is like a shell-game funnel of corporate money," one expert told Newsweek, speaking of the way big donors can support unpopular causes.
The Southern Poverty Law Center announced the lawsuit on Monday.
Its "flavorful splash removes foul executive orders."
"What happened in Charlottesville, and what is happening in communities across our country, demands our collective engagement to stand up to hate."
The crowdfunding campaign for the site and its editor, Andrew Anglin, aims to "stop SPLC's perfidious perjurers from destroying the alt-right's biggest website!"
President Trump has "unleashed right-wing hate in this country in a way that is difficult to remember," according to the Southern Poverty Law Center.