WASHINGTON

Democrats in the House of Representatives on Tuesday began Tuesday a second week of public hearings in the impeachment inquiry into U.S. President Donald Trump’s dealings with Ukraine.

Three days of hearings will see nine figures testify through Thursday. Three witnesses, including ousted top diplomat to Ukraine, Marie Yovanovitch, testified last week.

Tuesday

Jennifer Williams, an aide to Vice President Mike Pence, and National Security Council aide Lt. Col. Alexander Vindman will appeared before the House Intelligence Committee.

They listened in on Trump’s July 25 telephone call with Ukraine’s president, which is at the center of impeachment inquiry launched in September.

Democrats opened the inquiry against Trump on Sept. 24 following claims by a whistle-blower that the president tried to pressure Ukraine's President Volodymyr Zelensky to interfere in the 2020 presidential elections.

In the call, Trump allegedly made $400 million in military aid contingent Zelensky launching a probe into former U.S. Vice President Joe Biden, and his son, Hunter, a businessman, over unsubstantiated corruption allegations.

The elder Biden is a leading candidate in the race for the Democratic nomination to challenge Trump for the presidency in 2020.

Trump, a Republican, has accused Democrats of wasting time and said the inquiry is a “witch-hunt,” a “hoax” and maintains he did nothing wrong in his dealings with the eastern European nation.

Later in the day, former U.S. special envoy to Ukraine Kurt Volker and Tim Morrison, the top Russia adviser on White House National Security Council, will testify.

Wednesday

U.S. Ambassador to the European Union Gordon Sondland will appear Wednesday. He is viewed as the biggest witness this week.

Sondland acknowledged in a revised testimony in November that American military aid to Ukraine was contingent on officials there.

In a signed document, Sondland said he recalled a conversation in early September with Andriy Yermak, a Zelensky aide, in which he essentially lays out a quid pro quo with Ukraine that he had not acknowledged during closed-door testimony with House lawmakers Oct. 17.

Laure Cooper, the deputy assistant secretary of Defense for Russian, Ukrainian, and Eurasian Affairs, and David Hale, the undersecretary of state for political affairs, will testify after Sondland.

Thursday

Fiona Hill, the former top Russia expert at the White House, will testify along with David Holmes, an aide to top Ukraine diplomat Bill Taylor who testified last week.

In November, House impeachment investigators released a transcript in which she described former National Security Advisor John Bolton's backchannel communications with Ukraine.

"Rudy Giuliani is a hand grenade that is going to blow everybody up," Hill quoted Bolton told her referring to Trump's personal attorney.

Holmes also gave a deposition to the House committees conducting the impeachment inquiry. According to the transcript of the closed-door deposition, Holmes overheard the call between Trump and Sondland.