When asked if Blair would appear if Democrats subpoenaed him, Ellerman said he would not and that “direction from the White House and advice from DOJ cover subpoena.”

Blair is one of a slew of White House aides Democrats have called to the Hill this coming week as impeachment proceedings encroach further into the White House following testimony from top diplomats, State Department aides and officials with the National Security Council.

Officials also summoned to the Hill on Monday include John Eisenberg, deputy counsel to the president for national security affairs, Michael Ellis, senior associate counsel to the president, and Brian McCormack, associate director for natural resources, energy and science at the Office of Management and Budget, according to an official familiar with the impeachment inquiry.

It remains unclear which if any of those officials will show up. The White House has said it will not cooperate with the Democrats’ investigation.

Blair was brought into the White House less than one year ago by acting chief of staff Mick Mulvaney, along with several other top staffers from the Office of Management and Budget. Although Blair specialized in national security policy and spending and worked for several years on the Hill on appropriations, he worked out of the chief of staff’s office in the West Wing, where he served as a senior adviser to Mulvaney. In that capacity, he clashed often with the former National Security Adviser John Bolton and his team, according to a former senior administration official.