Watch LIVE: Trump Impeachment Hearings: Vindman, Williams, Volker and Morrison testify

Live Updates of the Impeachment Hearings: https://abcn.ws/2CWh2cr

Two White House national security aides who expressed concerns about a July phone call between President Donald Trump and Ukraine’s leader are appearing on Capitol Hill Tuesday, becoming the first current White House officials testify publicly in the Democrats’ impeachment investigation. Army Lt. Col. Alexander Vindman, the National Security Council’s Ukraine expert, will testify alongside Jennifer Williams, a national security aide to Vice President Mike Pence, in the morning.