"So by directing his subordinates to refuse to comply with the lawfully issued subpoenas — whether it’s for testimony or for documents — that’s an impeachable offense," Napolitano said. "We know that from history. Every time the House of Representatives has looked at that, with respect to a president, it has found it to be impeachable."

"On that, reasonable minds cannot disagree without rejecting history, rejecting constitutional norms," concluded Napolitano, a former New Jersey Superior Court judge.

The House Judiciary Committee on Wednesday held its first impeachment hearing, one day after the House Intelligence Committee released the report on its findings of an investigation of Trump.

Mulvaney is the White House chief of staff, while Pompeo is the secretary of State.

The Intelligence report did not include any recommendations for articles of impeachment, but it focused on what it said was obstruction by the administration, including through not allowing witnesses to testify, and through the intimidation of some witnesses.

If Trump is impeached in the House of Representatives, a two-thirds majority would be needed in the Senate for removal. Under that unlikely scenario, 20 GOP senators would need to defect in a Senate trial vote.

This story was updated at 4:35 p.m.