US Army Lieutenant Colonel Alexander Vindman (L), the top Ukraine expert on the National Security Council, arrives for a closed session before the House Intelligence, Foreign Affairs and Ov?ersight committees at the US Capitol in Washington, DC, USA, 29 October 2019. Lieutenant Colonel Vindman faces questions from the three congressional committees on a whistleblower's complaint that US President Donald J. Trump requested help from the President of Ukraine to investigate Joe Biden.