Williams is a State Department employee who is detailed to Pence's office and a career foreign service officer.
All of the witnesses testifying have already spoken to investigators in closed depositions, some of them for 10 hours or more.
Lt. Col. Alexander Vindman, the top Ukraine specialist on the National Security Council. In the call, Trump urged Zelensky to launch investigations into former Vice President Joe Biden and his son Hunter and into a debunked conspiracy theory about the 2016 USA presidential election.
Kurt Volker, the former special envoy to Ukraine, plans to tell lawmakers Tuesday that he was out of the loop at key moments during President Donald Trump's pressure campaign on Ukraine to turn up damaging information about Democrats, according to an account of his prepared testimony.
Trump attacked his former U.S. Ambassador to Ukraine in a tweet last week as she testified in the inquiry, claiming without substantiation that "everywhere Marie Yovanovitch went turned bad".
House Speaker Nancy Pelosi, a Democrat, said on Sunday in a CBS interview that Trump has every opportunity to present his case, including coming before intelligence committee hearings. Tim Morrison, the National Security Council's former director of Russian Federation and Europe will also testify.
"You've never spoken to the president and told him advice on Ukraine", Turner said.
US Supreme Court to hear Google bid to end Oracle copyright suit
Oracle says the Java APIs are freely available to those who want to build applications that run on computers and mobile devices. The Trump administration is backing Oracle at the Supreme Court and urged the justices to reject the appeal.
He also said Trump never christened him, Ambassador Gordon Sondland and Energy Secretary the "three amigos" in charge of Ukraine policy.
He said there is proof that Trump may have given untruthful responses.
"My predecessor [Fiona Hill] had a different style for managing her staff than I do", Morrison testified recently in the inquiry, after saying it wouldn't be unusual for Vindman to bring his concerns to Eisenberg. Williams works for the vice president and will testify on Tuesday. He added that there was "no doubt" about what Trump was asking Zelenskiy for.
Trump's weekend hospital visit was not on his public schedule.
Vindman, the top expert on Ukraine on the NSC, was on the July 25 call between US President Donald Trump and Ukrainian President Volodymyr Zelensky that sparked a whistleblower complaint and spiraled into the impeachment inquiry.
Tim Morrison, a White House aide with the National Security Council and who also heard the July phone call.
The second hearing will feature Volker, who the chairmen identify as having "played a direct role" in arranging meetings between Trump's personal attorney Rudolph Giuliani and Zelensky aides. He is also accused of asking Zelensky to investigate a debunked conspiracy theory about Ukrainian interference in the 2016 presidential election. Morrison said this irregular channel differed from the "normal process" that the USA government uses for foreign policy.