John Bolton, then the national security adviser, listens as President Trump speaks during a Cabinet meeting in February. Bolton's opposition to a pressure campaign to get Ukraine to investigate conspiracy theories may pit him against his former boss. Evan Vucci/AP hide caption
William Taylor, the acting U.S. ambassador to Ukraine, arrives on Tuesday at a closed session before the House Intelligence, Foreign Affairs and Oversight committees at the U.S. Capitol. Alex Wong/Getty Images hide caption
Former White House adviser on Russia Fiona Hill leaves the Capitol on Monday after testifying before lawmakers as part of the House impeachment inquiry into President Trump. Manuel Balce Ceneta/AP hide caption
Fiona Hill, a former White House adviser on Russia, arrives on Capitol Hill on Monday ahead of her testimony in connection with the House impeachment inquiry into President Trump. Andrew Harnik/AP hide caption