Trump started this with his racist birther lies, aimed at undermining a legitimate black president. He then made a series of racist attacks on other non-whites, and he also adopted an old racist slogan: America First. As a result, the KKK newspaper was almost the only newspaper to endorse Trump for President. (The other was owned by a large Republican backer.)
All of this is ultimately about white supremacists holding on to or regaining lost privileges and demonizing anybody who isn't white.