Washington (CNN) President Donald Trump on Sunday lashed out at a State Department employee who is set to testify publicly this week before lawmakers, the latest in a series of social media attacks made by the President against those cooperating in the House impeachment inquiry .

Tweeting a day after Williams' earlier, closed-door testimony was released, Trump urged Williams to "read BOTH transcripts of the presidential calls."

During a closed-door deposition earlier this month, Williams told lawmakers she was in the White House Situation Room listening to Trump's July 25 phone call with Ukrainian President Volodymyr Zelensky in real time and reviewed a transcript of Trump's April call prior to Pence's own April call with Zelensky. Williams also listened to a second call between Pence and Zelensky, which took place on September 18 after the hold on security assistance was lifted.

Trump's July 25 call is at the center of the impeachment inquiry, in which a whistleblower complaint alleges Trump asked for dirt on former Vice President Joe Biden, a 2020 presidential rival, and his son Hunter Biden. There is no evidence of wrongdoing by either Biden in Ukraine.

Williams testified that Trump's request for specific investigations struck her as "unusual and inappropriate" and "shed some light on possible other motivations" for Trump's decision to freeze security aid to Ukraine.

Pence's office on Sunday declined to defend Williams after Trump's Twitter attack.

"Jennifer is a State Department employee," Pence's press secretary Katie Waldman said in response to CNN's request for comment.

Like many foreign policy advisers at the White House, Williams is a State Department employee detailed to Pence's office.

Staffers in the vice president's office have made a concerted effort to distance Pence from Williams, even before she sat down to testify. But sources explained to CNN that his office is selective about which career officials get detailed to their staff. His senior staff typically interviews them beforehand.

Keith Kellogg, the vice president's national security adviser, was responsible for selecting Williams.

CNN has reached out to Williams and her attorney for comment, but has not received a response.

She is currently serving as a special adviser to the vice president for Europe and Russia. Current and former colleagues have praised Williams, with one White House official saying: "She is the most professional person in this building."