For only the fourth time in U.S. history, the House of Representatives has started a presidential impeachment inquiry .
House committees are trying to determine if President
Donald Trump violated his oath of office by asking
Ukraine to investigate political rival
Joe Biden and his family, and to investigate the country's involvement in the 2016 U.S. presidential election.
The three House committees leading the
Democratic investigation have scheduled several current and former National Security Council officials to testify this week behind closed doors — an attempt to get a better look inside the
White House as Trump pushed Ukraine to conduct politically motivated investigations.