Sen. Kamala Harris (D-Calif.) and a large group of Democratic senators have signed a letter that will be sent to the White House on Monday calling on President Donald Trump to fire senior adviser Stephen Miller in light of leaked emails showing the extent of his white nationalist beliefs.

We write to demand the immediate removal of Stephen Miller as your advisor, states the letter, a copy of which was provided to HuffPost by Harris office.

The leaked emails, the letter says, show that what is driving Mr. Miller is not national security, its white supremacysomething that has no place in our country, federal government, and especially not the White House.

Simply put, the letter continues, Mr. Miller is unfit to serve in any capacity at the White House, let alone as a senior policy adviser.

Harris, the second Black woman to ever serve in the U.S. Senate (who ended her presidential campaign last week), is the lead signatory of the letter. Twenty-six other senators signed, including five presidential candidates: Elizabeth Warren (D-Mass.), Cory Booker (D-N.J.), Bernie Sanders (I-Vt.), Amy Klobuchar (D-Minn.) and Michael Bennet (D-Colo.).

The letter adds to growing and prolonged pressure on the White House to get rid of Miller, the aide credited with developing the Trump administrations brutal anti-immigrant policies.

Nearly one month ago, the Southern Poverty Law Center published a series of blockbuster reports analyzing 900 emails Miller sent to the far-right website Breitbart from 2015 to 2016, when he was working as an aide to then-Sen. Jeff Sessions (R-Ala.). The emails show Miller actively shaping Breitbart stories related to race and immigration, encouraging editors and writers at the publication to draw inspiration from explicitly white supremacist websites like VDare.

At one point Miller suggested that Breitbart write about The Camp of Saints , a fascist French novel that depicts feces-eating brown people taking over Europe.

It is simply appalling that a senior advisor to the President advanced parallels between this book and contemporary events, states the letter the senators sent to the White House on Monday.