Dozens of House Democrats called on the White House Thursday to fire senior adviser Stephen Miller, citing a left-wing group's claims that he promoted "white nationalist" content in leaked emails.

"We formally request that you immediately remove White House Senior Advisor Stephen Miller from your administration," a letter sent to the White House read. "A documented white nationalist has no place in any presidential administration, and especially not in such an influential position."

Miller, who has been with Trump since his 2016 campaign, has been singled out for his role in pushing Trump's hard-line immigration agenda within the administration.

The list of Democrats included who signed the letter included party leaders like House Judiciary Chairman Jerrold Nadler, D-N.Y., and Chief Deputy Whip Dan Kildee, D-Mich. In total, 107 signed the letter and were led by Rep. Don Beyer, D-Va., as well as "Squad" member Reps. Ilhan Omar, D-Minn. Her fellow "Squad" members, Rep. Alexandria Ocasio-Cortez, D-N.Y., and Rashida Tlaib, D-Mich, signed on as well.

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“Miller’s emails and the sentiments expressed in them are incompatible with public service and render him unfit to shape any policy – immigration or otherwise. We refuse to tolerate white nationalism and xenophobia in the White House or elsewhere in the United States. Mr. Miller must be fired immediately," the Democrats said.

They added that Miller had a "white supremacist" influence on Trump's policies -- specifically his position on Dreamers and effort to lower the ceiling for refugee admissions.

Their letter came after the Southern Poverty Law Center (SPLC) -- a left-wing group known for accusing conservatives of "hate" -- published its findings from more than 900 emails it obtained from former Breitbart editor Katie McHugh.

The SPLC report claimed Miller emailed Breitbart, a conservative news platform, more than 900 times between 2015 and 2016. The non-profit claims the emails showed Miller “promoted white nationalist literature, pushed racist immigration stories and obsessed over the loss of Confederate symbols” following the 2015 Charleston, S.C., church shooting. (The gunman in that attack was a white supremacist and killed nine African-Americans.)

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It also claimed that Miller shared white nationalist websites, a “white genocide”-themed novel, xenophobic conspiracy theories and eugenics-era immigration laws that Adolf Hitler lauded in “Mein Kampf.” The report concludes the emails show that Miller used these ideologies to “as an architect” for Trump administration immigration policies, included the travel ban, a zero-tolerance policy which resulted in the separation of children at the border, and undocumented immigrant arrest quotas.

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White House Press Secretary Stephanie Grisham defended Miller on Tuesday, though, after former Democratic presidential nominee Hillary Clinton said his presence in the White House was an "emergency."

"Stephen Miller is dedicated to this country and I am proud to work alongside him every single day with the goal of making our nation even greater. He is a friend and colleague, and we are lucky to have him in the White House," she said.

Fox News' Danielle Wallace contributed to this report.