Donald Trump's former White House adviser Stephen Miller was exposed by an investigative journalist on MSNBC on Saturday.

Miller, who directed Trump's border policy during the ex-president's term in office, has since then been waging his own private war against diversity and programs promoting inclusion. But he wasn't always like that, according to investigative journalist Jean Guerrero.

Guerrero, the author of "Hatemonger: Stephen Miller, Donald Trump, and the White Nationalist Agenda," appeared on MSNBC to profile the man behind Trump's border agenda.

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"What is his vision for America?" asked the host, who described Miller as a "mastermind."

"His vision is a white nationalist America and this agenda you described is something he has been dreaming about for a very long time," she said. "In my book, I trace how he was radicalized as a teenager by far-right provocateurs who believe racism against Black and brown people was not a problem and that the real problem in American society was racism against whites."

She continued:

"This is an idea that originated with white supremacists like David Duke who in the 1970s was calling white men the 'real second class citizens in America.' But while back then, it was largely rejected and fringe; in 2024, it is mainstream GOP politics thanks to Stephen Miller."

Watch the whole interview below or click the link here.