President Donald Trump took to Twitter Sunday to lash out at a State Department aide to Vice President Mike Pence who is set to testify publicly this week in the House Impeachment inquiry, labeling her a "Never Trumper."

Jennifer Williams is a career foreign service officer in the State Department who is detailed to Pence's office as an adviser for Europe and Russia. Williams was among the staffers in the White House Situation Room who listened and took notes during Trump's July 25 call when Trump asked Ukraine President Volodymyr Zelenskiy for “a favor.” A whistleblower’s complaint about that call helped spark the House impeachment investigation.

Transcripts from the closed-door testimony from Williams were released Saturday. Williams testified that Trump's discussion on the call of specific investigations struck her as "unusual and inappropriate" and seemed to point to "other motivations" for holding up the military aid.

After the call, Williams told investigators, she put the White House’s rough transcript into the vice president's daily briefing book.

"I just don't know if he read it," she said.

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Williams corroborated the testimony of a previous witness, Lt. Col. Alexander Vindman, an NSC aide on the call, who said the White House dropped the word “Burisma” from the transcript. She said in an addendum to her testimony that Zelenskiy had mentioned the word “Burisma” in the call.

Vindman and Williams are scheduled to testify together during a public impeachment hearing on Tuesday morning.

"Tell Jennifer Williams, whoever that is, to read BOTH transcripts of the presidential calls, & see the just released ststement from Ukraine. Then she should meet with the other Never Trumpers, who I don’t know & mostly never even heard of, & work out a better presidential attack!" Trump tweeted Sunday morning.

The criticism of Williams comes two days after Trump used Twitter to call out ousted U.S. Ambassador to the Ukraine Marie Yovanovitch while she was in the middle of testifying publicly Friday.

“I can’t speak to what the president is trying to do, but I think the effect is to be intimidated,” she said in response.