Fiona Hill, who worked as a top Russia analyst on the National Security Council staff until this summer, testified under subpoena for roughly 10 hours on Monday, as part of the ongoing impeachment inquiry.
She is the third witness to have appeared for a closed-door session in front of the three House committees conducting the formal impeachment proceedings, soon after former Ukraine special envoy Kurt Volker and former US Ambassador to Ukraine, Marie Yovanovitch.
Democrats have claimed that Hill corroborated what they described as a concerted effort by Trump allies to remove Yovanovitch from her post in May, with Rudy Giuliani reportedly being central to the effort.
"Rudy Giuliani has clearly been a leading force for the administration in defining a shadow foreign policy in Ukraine. There was an official foreign policy, which was attempting to counter corruption in Ukraine", said Rep. Jamie Raskin (D-Md.), a member of the House Oversight and Reform Committee. "So you had two foreign policies that were working completely against each other".
Hill had notably stepped down days before the now-infamous transcribed phone call between POTUS and his Ukrainian counterpart that prompted the Democrats' impeachment inquiry, after they suspected Trump of having asked a foreign country to dig up dirt on his political rival, Joe Biden, ahead of the 2020 presidential vote in exchange for the continuation of US military aid.
Hill is known to have worked closely with Yovanovitch and was expected to express concerns about the abrupt removal of the Ukrainian ambassador, which both the whistleblower, who initially complained about the phone call and Yovanovitch herself said had political grounds.
Following Hill's testimony, Democrats claimed her words only underpinned the anti-Trump allegations, adding that Hill gave the impression of being a highly credible civil servant:
"Her recall of meetings and content and who was there, with such specificity, was in some ways extraordinary", Rep. Harley Rouda (D-Calif.), a member of the House Oversight and Reform Committee, later said.
"A true patriot", he added. "I found her to be very credible".
Marie Yovanovitch likewise testified in front of the committees last week, saying Trump allies staged a "concerted campaign" against her based on "unfounded and false claims by people with clearly questionable motives".
She told investigators that Deputy Secretary of State John Sullivan made it clear that she "had done nothing wrong", and her sacking was unlike that of other ambassadors.
Hill's testimony has opened a busy week for Democratic investigators, who, despite a backlash from Republicans calling for hearings to be public and transparent to the maximum, insist that if the hearing is made public, witnesses will align their testimonies. Republicans,
Rep. Lee Zeldin (R-N.Y.) among others, took a dig at selective media leaks from hearings that emerged afterwards, arguing they weren't reflective of grand jury proceedings and echoing other Republicans in requesting that transcripts of each closed-door session be made public.
"In a grand jury trial, you don't come out and leak anything that you heard that's favourable, to try to have a story spun as positively as you can", Zeldin said.
The next in line to testify is George Kent, deputy-assistant secretary of state, followed by Michael McKinley, a former State Department adviser, and Gordon Sondland, the ambassador to the European Union, who is set to appear under subpoena on Thursday after the State Department blocked him from testifying last week.
US President Donald Trump has been embroiled in a scandal surrounding his July call with Ukrainian President Volodymyr Zelensky, in which he allegedly pressed his counterpart to investigate 2020 Democratic candidate Joe Biden and his son, that he alleged were involved in a shadow corruption scheme tied to Hunter's business dealings in Ukraine, as a board member of a natural gas firm.
Zelensky commented on the matter, saying the call was productive and there was by far no pressure exerted on him, cheekily noting the only person capable of pressuring him was his little son.
The Ukraine call triggered an impeachment procedure against Trump in late September, with POTUS repeatedly asserting that his conversation with Zelensky was absolutely legal - a "perfect" exchange that contained no impeachable offences.