Senate Democrats are demanding that President Trump Donald John TrumpBiden says voters should choose who nominates Supreme Court justice Trump, Biden will not shake hands at first debate due to COVID-19 Pelosi: Trump Supreme Court pick 'threatens' Affordable Care Act MORE fire Stephen Miller Stephen MillerSpecial counsel investigating DeVos for potential Hatch Act violation: report Trump confirms another White House staffer tested positive for COVID-19 Biden pick creates furor, underscoring bitterness over Obama immigration policy MORE after a watchdog group released hundreds of controversial emails the White House adviser sent prior to his time in the administration.

Twenty-seven Democrats, led by Sen. Kamala Harris Kamala HarrisPelosi: Trump Supreme Court pick 'threatens' Affordable Care Act What Kamala Harris' VP nomination means to us Harris slams Trump's Supreme Court pick as an attempt to 'destroy the Affordable Care Act' MORE (D-Calf.), sent Trump a letter on Monday calling for Miller's "immediate removal."

"Recent reports confirm that he advanced white nationalist, anti-immigrant ideologies. Continuing to employ him as the senior architect of your immigration policies ensures that those policies discriminate against individuals of color to advance white nationalist ideals. He must be removed," the senators wrote.

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The letter is the latest from Democrats and civil rights groups calling for Miller to be fired after the Southern Poverty Law Center (SPLC) published summaries of emails the White House aide sent in 2015 and 2016 when he worked as an aide to then-Sen. Jeff Sessions Jefferson (Jeff) Beauregard SessionsRoy Moore sues Alabama over COVID-19 restrictions GOP set to release controversial Biden report Trump's policies on refugees are as simple as ABCs MORE (R-Ala.).

The emails contain links and references to publications associated with white nationalism and show how Miller coordinated with Breitbart News to shape coverage around immigration and the 2016 GOP presidential primary.

The White House has stood behind Miller despite the swirl of controversy, calling the SPLC "discredited."

Spokespeople for the White House didn't immediately respond to a request for comment on Monday about the new letter from Senate Democrats.

Democrats argued in their letter that Miller's "demonstrable white nationalist ideology" has influenced Trump's agenda, particularly on immigration policy.

"These e-mails clearly show what is driving Mr. Miller. It’s not national security, it’s white supremacy—something that has no place in our country, federal government, and especially not the White House. ... Simply put, Mr. Miller is unfit to serve in any capacity at the White House, let alone as a senior policy adviser. We demand that you remove Stephen Miller immediately," they added.

More than 100 House Democrats called late last month for Miller to resign. More than 50 civil rights groups have also sent a separate letter calling on Trump to fire Miller.