In the letters, the heads of the three committees said they had been told by the lawyers that their clients would not appear because a White House lawyer could not be present - one of the points that Trump and Republicans in Congress have used to try and describe the Democrats' impeachment process as a "sham". They painted a detailed picture of the distress felt by top USA diplomats as Trump allies tried to pressure Ukraine to launch investigations into the Republican president's domestic political rivals.
Vindman sat in on the July 25 call between Trump and Ukraine President Volodymyr Zelenskiy that spurred the House of Representatives' impeachment investigation. "Why is the White House counsel telling people not to talk about it?" The NSC aide said that Eisenberg approached him several days after the call and said that a CIA employee had raised internal concerns about the call, and that the agency's top lawyer had relayed those concerns to the White House, people familiar with the testimony said.
Vindman's testimony Tuesday pointed to several actions by White House officials that could be interpreted as attempts to cover up Trump's conduct.
President Trump appeared to warn reporters last night of the upcoming release of information on Lt. Col. Vindman that will prove he really is a "Never-Trumper".
Vindman testified that he found it improper to demand a foreign government investigate a US citizen and was so anxious about the implications that he took the matter to Eisenberg.
"I would certainly say I'd invite him", Trump said, according to The New York Times.
The directive from Eisenberg adds to an expanding list of moves by senior White House officials to contain, if not hide, possible evidence of Trump's attempt to pressure Ukrainian President Volodymyr Zelensky to provide information that could be damaging to former vice president Joe Biden.
Eisenberg has three titles, which is rare, Mukasey said.
New details from Vindman's testimony also shed light on other aspects of the tense aftermath of the call inside the White House. Burck referenced a lawsuit filed by former deputy national security Charles Kupperman, who is seeking a court ruling on whether he needed to comply with the Congressional request to appear or the White House instruction to stay away.
Other officials who have been called this week are not expected to appear.
The committees began releasing interview transcripts as they prepare for public hearings that could start this month.
In his statement to lawmakers this week, Vindman said, "I do not know who the whistleblower is and I would not feel comfortable to speculate".
"If you have the president's son saying, you know, we need to pull these clowns, or however he referred to me, it makes it hard to be a credible ambassador in a country", she said.
Joe Biden in 2016 pressured then-Ukrainian President Petro Poroshenko into ousting Viktor Shokin, a prosecutor who was probing Hunter Biden's employer Burisma.
This report doesn't really add to the facts that we know about the July 25th phone call, of course, but it does corroborate both the whistleblower's complaint about the extent to which the White House sought to suppress evidence of the call and the reports that have come out from other witnesses on that same issue.
"What I said on the phone call with the Ukrainian President is "perfectly" stated", Mr Trump said on Twitter.