Rep. Elijah Cummings, the chairman of the House Oversight and Reform Committee, has invited top White House policy aide Stephen Miller, best known for his hardline positions on immigration, to testify before his committee May 1.

Miller, as CBS News' chief Washington correspondent Major Garrett has reported, is behind an overhaul of the Department of Homeland Security (DHS). Cummings' request for testimony — which Miller is likely to deny, at least initially — comes as the president is considering sending detained illegal immigrants to sanctuary jurisdictions and closing large sections of the border.

"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 a letter to Miller.

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"I want to make clear that I am inviting you to appear voluntarily," Cummings continued. "I am offering you an opportunity to make your case to the committee and the American people about why you — and presumably President Trump — believe it is good policy for the Trump administration to take 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."

Mr. Trump praised Miller last week, while making it clear to reporters that only one person is in charge of immigration policy and DHS — him.

Asked if he has ever considered making Miller DHS secretary, Mr. Trump responded, "No, Stephen is an excellent guy. He's a wonderful person. People don't know him. He's a wonderful — been with me from the beginning. He's a brilliant man. And, frankly, there's only one person that's running it. You know who that is? It's me."

Cummings gave Miller until April 24 to respond.