House Democrats have urged controversial Trump aide Stephen Miller to testify in Congress to publicly defend his aggressive crackdown on both legal and illegal immigration. Miller has become increasingly influential in the White House on immigration—he was the man behind Donald Trump’s Muslim travel ban and the forced separation policy. “I understand that you may not want to submit yourself to rigorous questioning,” Rep. Elijah Cummings, D-Md., chairman of the House Oversight and Reform Committee, wrote in a letter to Miller Wednesday. “I want to make clear that I am inviting you to appear voluntarily ... 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 actions it has.” Cummings told Miller he wants him to testify in just two weeks on May 1. The White House is yet to respond to the invitation.