Kamala Harris and more than two dozen of her Senate colleagues are urging the White House to fire Stephen Miller, a senior adviser to President Trump who has heavily shaped the administration’s immigration policy, over his white supremacist beliefs.

In a letter the California Democrat will send to the White House on Monday along with 26 colleagues, she writes that Miller “is unfit to serve in any capacity at the White House, let alone as a senior policy adviser.” Huffington Post first reported the news.

Among those who signed on to the letter are 2020 presidential contenders Sens. Bernie Sanders (I-Vt.), Elizabeth Warren (D-Mass.), Cory Booker (D-N.J.), and Amy Klobuchar (D-Minn.). Harris dropped her bid last week, saying she didn’t have the funds to be competitive.

“What is driving Mr. Miller,” the letter says, is “not national security, it’s white supremacy — something that has no place in our country, federal government, and especially not the White House.”

“We write to demand the immediate removal of Stephen Miller as your advisor,” it reads.

Trump hired the 34-year-old Miller in January of 2016 as a senior adviser on his presidential campaign.

The letter comes after the Southern Poverty Law Center published a report that analyzed nearly 1,000 emails that Miller sent to the far-right website Breitbart between 2015 and 2016 while he was an aide to then-Sen. Jeff Sessions (R-Ala.).

In the emails, Miller urges Breitbart staff to read white nationalist websites and books for reporting inspiration, and laments the fact that Amazon stopped selling Confederate flags. He has also told border officials that it is his goal to make migrants’ lives as difficult as possible.

The emails published by Southern Poverty Law Center further illuminate Miller’s xenophobic and racist ideologies –– for example, his recommendation of a book about white genocide that is perpetrated by people of color who eat feces –– thinking that has shaped his work in the Trump administration.

In their letter to the White House, Harris and her colleagues list the immigration policies that Miller is widely credited with implementing, including a ban on travel into the U.S. from six predominantly Muslim countries, as well as a practice that saw border officers separating infants and teenagers alike from their immigrant parents.

“The Muslim ban targeted individuals of color and caused chaos at U.S. airports around the country, wreaking havoc on the lives of countless individuals and families,” the letter says. “The family separation policy tore children from their families, resulting in widely reported mistreatment and human rights abuses of immigrants in detention facilities nationwide. The rescission of Deferred Action for Childhood Arrivals (DACA) has thrown the lives of hundreds of thousands of DREAMers into chaos and instability.”

It continues: “Mr. Miller has also reportedly advanced your administration’s efforts to slash refugee admissions, limit asylum access for vulnerable populations, prevent extensions of Temporary Protected Status to those granted safety from humanitarian crises abroad, and disqualify immigrants who use public resources from receiving certain immigration benefits,” it continues.

Harris and her Senate colleagues aren’t the only elected Democrats who are seeking Miller’s removal from office. Over 80 Democrats in the House have said Miller should resign, and New York Rep. Alexandria Ocasio-Cortez has started an online petition to demand his resignation.