(WASHINGTON) — Two White House national security aides who expressed concerns about a July phone call between President Donald Trump and Ukraine’s leader will appear on Capitol Hill Tuesday, becoming the first current White House officials to testify publicly in the Democrats’ impeachment investigation. Lt. Col. Alexander Vindman, the National Security Council’s Ukraine expert, will testify alongside Jennifer Williams, a national security aide to Vice President Mike Pence, Tuesday morning. Both officials listened in on Trump’s July 25 phone call with Ukrainian President Volodymyr Zelenskiy. Vindman and Williams have also come under attack from the president for offering their accounts to Congress.

Here is how the day is unfolding:8:15 a.m. Army Lt. Col. Alexander Vindman, the first witness, has arrived in Capitol Hill in his dress blue uniform. He was accompanied by his brother, Yevgeny, who is also serves on the National Security Council as an ethics lawyer.

Vindman told investigators, according to a transcript of his closed session, that he was “concerned” by the call, adding that he “did not think it was proper to demand that a foreign government investigate a U.S. citizen,” a reference to the suggestion from Trump that Ukraine investigate former Vice President Joe Biden’s son, Hunter Biden, and his work for Ukrainian energy company Burisma. He also told lawmakers there was “no doubt” in his mind about what Trump sought from Ukraine in the July phone call with Zelenskiy.In his private testimony, Vindman also told lawmakers he repeatedly raised his concerns about the president’s comments — along with the discussion of the investigations that Rudy Giuliani, Trump’s personal lawyer, was publicly calling for — with NSC lawyers.He also said he attempted to get nearly $400 million in military aid to Ukraine restored after it was put on hold over the summer, drafting a memo that the president refused to sign.The Iraq War veteran, who received a Purple Heart, is expected to appear in uniform.Williams said in a separate closed session with lawmakers that she found the mention of investigations into the 2016 election and unsubstantiated theories of Ukraine’s meddling in the race, and a probe into the Biden family’s dealings in Ukraine “unusual and inappropriate.”The president has lashed out at both officials, calling Vindman a “never Trumper” as he testified to Congress last month, and criticizing Williams after her closed-door testimony was released over the weekend.Tim Morrison, a departing NSC official who was also on the Trump-Zelenskiy call, will testify Tuesday afternoon. While he raised concerns about the call to White House lawyers — specifically, how a leak of the transcript would be received in a polarized Washington, and impact bipartisan support for Ukraine — he previously told impeachment investigators that he was “not concerned that anything illegal was discussed,” according to a transcript of his deposition released by House Democrats.Lawmakers will also question former U.S. envoy to Ukraine Kurt Volker on Tuesday afternoon.Republicans, who requested the public testimony from both officials, believe elements of their accounts undermine Democrats’ concerns about the withholding of aid for investigations at the center of the impeachment inquiry.Tuesday’s testimony could set the stage for the upcoming appearance of Gordon Sondland, Trump’s ambassador to the European Union and an apparent central player in the efforts to encourage Ukraine to launch investigations that could benefit Trump politically.The House Intelligence Committee is scheduled to hold a total of five public hearings this week with nine witnesses.Sondland will testify Wednesday morning, followed by senior Defense Department and State Department officials Laura Cooper and David Hale.Fiona Hill, the NSC’s former Russia expert under former national security adviser John Bolton, is scheduled to appear on Capitol Hill Thursday morning, along with Holmes.

Copyright © 2019, ABC Audio. All rights reserved.