House Oversight and Reform Committee Chairman Elijah Cummings Elijah Eugene CummingsBlack GOP candidate accuses Behar of wearing black face in heated interview Overnight Health Care: US won't join global coronavirus vaccine initiative | Federal panel lays out initial priorities for COVID-19 vaccine distribution | NIH panel: 'Insufficient data' to show treatment touted by Trump works House Oversight Democrats to subpoena AbbVie in drug pricing probe MORE (D-Md.) sent a letter on Wednesday asking White House senior adviser 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 to testify before the panel.

“I am inviting you to testify before the Committee because it appears that you are one of the primary moving forces behind some of the most significant — and in my view, troubling — immigration policies coming out of the Trump White House,” Cummings wrote in his letter.

“I am offering you an opportunity to make your case to the Committee and the American people about why you — and presumably President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE — believe it is good policy for the Trump Administration to take the actions it has, including intentionally separating immigrant children from their parents at the border to deter them from coming to the United States, transferring asylum seekers to sanctuary cities as a form of illegal retribution against your political adversaries, and firing top Administration officials who refuse orders to violate the law,” he added.

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Cummings requested that Miller respond to his invitation by April 24.

The White House did not immediately respond to a request for comment from The Hill.

Miller, a former Senate aide, has pushed for hard-line immigration policies in the Trump administration, emerging as a key player amid recent turnover at the Department of Homeland Security (DHS).

Trump has praised Miller but denied that he has driven the administration's immigration policy.

Rep. Jerrold Nadler Jerrold (Jerry) Lewis NadlerDemocrats shoot down talk of expanding Supreme Court Schumer: 'Nothing is off the table' if GOP moves forward with Ginsburg replacement Top Democrats call for DOJ watchdog to probe Barr over possible 2020 election influence MORE (D-N.Y.), the chairman of the House Judiciary Committee, also said this week that Miller should appear before Congress.

“Probably Stephen Miller, who seems to be the boss of everybody on immigration, ought to come before Congress and explain some of these policies,” Nadler said Sunday on CNN’s “State of the Union.”

Beyond the most recent immigration proposals from the administration, Miller was also a staunch proponent of the White House’s decision to implement a travel ban from several majority-Muslim countries and lower the number of refugees allowed in the country.

Miller has only seen his stature rise in the administration amid rolling changes in top positions at DHS. The White House staffer was reportedly a driving force behind the president’s decision to dismiss former Homeland Security Secretary Kirstjen Nielsen Kirstjen Michele NielsenMore than million in DHS contracts awarded to firm of acting secretary's wife: report DHS IG won't investigate after watchdog said Wolf, Cuccinelli appointments violated law Appeals court sides with Trump over drawdown of immigrant protections MORE and also pushed for the removal of U.S. Citizenship and Immigration Services Director Lee Cissna and DHS General Counsel John Mitnick.

Immigrant rights groups and even some people close to Trump have expressed concern with Miller’s outsize role in the White House, saying his hard-line policies could exacerbate issues at the border and worsen relationships with Democrats on Capitol Hill.

"[Trump] is listening and coordinating with a guy who has never had legislative success as a staffer," a Trump loyalist who advised the campaign told The Hill recently. "We are going to end up with the same result every time."