A staff member wheels a cart full of documents into the committee room before the start of a House Judiciary Committee hearing on the impeachment Inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., December 4, 2019.

Members of the House Judiciary Committee are reflected in a television monitor as they begin their first hearing on the impeachment inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., December 4, 2019.

The U.S. Capitol building is seen before a House Judiciary Committee hearing on the impeachment inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., December 4, 2019.

Signs with quotes from Democratic members of Congress sit behind Republican before the start of a House Judiciary Committee hearing on the impeachment Inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., December 4, 2019.

Witness Jonathan Turley, a professor of law at George Washington University Law School, takes his seat surrounded by photographers as he arrives to testify at the start of a House Judiciary Committee hearing on the impeachment Inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., December 4, 2019.

U.S. House Judiciary Committee Chairman Jerrold Nadler (D-NY) speaks with Republican ranking member Rep. Doug Collins (R-GA) during a House Judiciary Committee hearing on the impeachment Inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., December 4, 2019. Saul Loeb/Pool via REUTERS

A U.S. Capitol police officer watches from the back wall of the hearing room as the House Judiciary Committee holds their first hearing on the impeachment inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., December 4, 2019.

U.S. Rep. Matt Gaetz (R-FL) smiles as he sits beside U.S. Rep. Jim Sensenbrenner (R-WI) in front of Rep. Mike Johnson (R-LA) during the first House Judiciary Committee hearing on the impeachment inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., December 4, 2019.

U.S. Representative Sheila Jackson Lee holds up copies of the Mueller Report as she questions constitutional scholars during a House Judiciary Committee hearing on the impeachment Inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., December 4, 2019. Saul Loeb/Pool via REUTERS

Pamela Karlan, co-director of the Supreme Court Litigation Clinic at Stanford University Law School, sits among witnesses Noah Feldman, a professor of law at Harvard University Law School; Michael Gerhardt, professor of law at University of North Carolina School of Law; and Jonathan Turley, professor of law at George Washington University Law School, during a House Judiciary Committee hearing on the impeachment Inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., December 4, 2019.

Republican House members Rep. Louie Gohmert (R-TX), Rep. Mike Johnson (R-LA), Rep. Jim Jordan (R-OH), Rep. Andy Biggs (R-AZ) and Rep. Matt Gaetz (R-FL) confer during a break as the House Judiciary Committee holds their first hearing on the impeachment inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., December 4, 2019.

House Judiciary Committee Chairman Jerrold Nadler (D-NY) speaks at the start of a House Judiciary Committee hearing on the impeachment Inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., December 4, 2019.

The U.S. Capitol building is seen before a House Judiciary Committee hearing on the impeachment inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., December 4, 2019.

The Washington Monument is seen during morning sunrise, ahead of a House Judiciary Committee impeachment hearing on Capitol Hill in Washington, D.C., U.S., December 4, 2019.

Members of the news media line up outside of the hearing room, ahead of a House Judiciary Committee impeachment hearing on Capitol Hill in Washington, D.C., U.S., December 4, 2019.

Atrtendee gather in the audience for the start of a House Judiciary Committee hearing on the impeachment Inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., December 4, 2019.

Rep. Jim Jordan (R-OH) arrives for the start of a House Judiciary Committee hearing on the impeachment Inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., December 4, 2019.

U.S. House Judiciary Committee Chairman Jerrold Nadler (D-NY) swears-in the witnesses during a House Judiciary Committee hearing on the impeachment of U.S. President Donald Trump on Capitol Hill in Washington, DC, December 4, 2019. Saul Loeb/Pool via REUTERS

Pamela Karlan, professor of Public Interest Law and co-director of the Supreme Court Litigation Clinic at Stanford Law School, listens to Noah Feldman, professor of law and director of the Julis-Rabinowitz Program on Jewish and Israeli Law at Harvard Law School, as he testifies during a House Judiciary Committee hearing on the impeachment inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., December 4, 2019.

Pamela Karlan, professor of Public Interest Law and co-director of the Supreme Court Litigation Clinic at Stanford Law School, is seated during a break in testimony before a House Judiciary Committee hearing on the impeachment inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., December 4, 2019.

Members of the audience stand awaiting the start of a House Judiciary Committee hearing on the impeachment Inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., December 4, 2019.

U.S. Rep. Matt Gaetz (R-FL) questions a panel of constitutional experts during a House Judiciary Committee hearing on the impeachment Inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., December 4, 2019. Saul Loeb/Pool via REUTERS

Witness Jonathan Turley, a professor of law at George Washington University Law School, takes his papers from his briefcase as he prepares to testify at the start of a House Judiciary Committee hearing on the impeachment Inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., December 4, 2019.

Pamela Karlan, professor of Public Interest Law and co-director of the Supreme Court Litigation Clinic at Stanford Law School, testifies during a House Judiciary Committee hearing on the impeachment inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., December 4, 2019.

Jonathan Turley, professor of law at George Washington University Law School, testifies during a House Judiciary Committee hearing on the impeachment inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., December 4, 2019.

Witnesses Noah Feldman, professor of law at Harvard University Law School, Pamela Karlan, co-director of the Supreme Court Litigation Clinic at Stanford University Law School, Michael Gerhardt, professor of law at University of North Carolina School of Law and Jonathan Turley, professor of law at George Washington University Law School appear to testify at the first U.S. House Judiciary Committee hearing on the impeachment inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., December 4, 2019.

U.S. Representative Zoe Lofgren (D-CA) attends a House Judiciary Committee hearing on the impeachment Inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., December 4, 2019. Saul Loeb/Pool via REUTERS

Members of the public use binoculars as they watch the House Judiciary Committee hearing on the impeachment Inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., December 4, 2019. Saul Loeb/Pool via REUTERS

A U.S. Capitol police officer watches from in front of a video monitor displaying definitions of "High Crimes and Misdemeanors" as the U.S. House Judiciary Committee holds their first hearing on the impeachment inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., December 4, 2019.

The U.S. Capitol Rotunda is seen reflected off a window of a vehicle, during sunrise, ahead of a House Judiciary Committee impeachment hearing on Capitol Hill in Washington, D.C., U.S., December 4, 2019.

Ranking member Rep. Doug Collins (R-GA) shakes hands with Democratic member of the committee Jamie Raskin (D-MD) prior to the start of a House Judiciary Committee hearing on the impeachment Inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., December 4, 2019.

Witnesses Noah Feldman, a professor of law at Harvard University Law School, Pamela Karlan, co-director of the Supreme Court Litigation Clinic at Stanford University Law School, Michael Gerhardt, professor of law at University of North Carolina School of Law and Jonathan Turley, professor of law at George Washington University Law School are sworn in to testify at the start of a House Judiciary Committee hearing on the impeachment Inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., December 4, 2019.

Noah Feldman, a professor of law at Harvard University Law School, testifies as the U.S. House Judiciary Committee holds their first hearing on the impeachment inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., December 4, 2019.

Rep. Zoe Lofgren (D-CA) listens as constitutional scholars testify before the House Judiciary Committee hearing on the impeachment Inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., December 4, 2019. Drew Angerer/Pool via REUTERS

The U.S. Capitol Rotunda is seen during sunrise, ahead of a House Judiciary Committee impeachment hearing on Capitol Hill in Washington, D.C., U.S., December 4, 2019.

House Judiciary Committee Chairman Jerry Nadler (D-NY) takes his seat beside Republican ranking member Rep. Doug Collins (R-GA) at the start of a committee hearing on the impeachment Inquiry into U.S. President Donald Trump on Capitol Hill in Washington, U.S., December 4, 2019.