Lieutenant Colonel Alexander Vindman, the White House's top Ukraine expert, testified before the committees overseeing the impeachment inquiry against President Donald Trump on Tuesday.
Vindman was a firsthand witness to the July 25 phone call, in which Trump pressured Ukrainian President Volodymyr Zelensky to investigate Trump's political rival, former Vice President Joe Biden.
The White House released a rough transcript of the phone call last month, but in his closed-door testimony, Vindman told lawmakers that he was kept from adding additional clarifying details to the transcript, such as Trump mentioning recordings of Biden talking about corruption in Ukraine and Zelensky mentioning Burisma Holdings, the Ukraine-based energy company which employed Biden's son.
While the transcript was always known to be a rough transcript, rather than a word-for-word record of the phone call, Vindman's testimony sparked additional concerns about the White House's attempts to cover up the phone call by transferring the word-for-word transcript to a separate, classified network.
Tim Morrison, an NSC member overseeing Russia and Europe, who was also listening on the call, is set to testify on Thursday.