The United States House of Representatives entered a new and critical phase in the impeachment inquiry of President Donald Trump on Wednesday with the first public hearing of the probe.
The House Intelligence Committee is hearing from William Taylor, the top diplomat in Ukraine, and George Kent, the deputy assistant secretary of state for European and Eurasian Affairs.
Democrats have accused Trump of abusing the power of the presidency by withholding political support and US security assistance from Ukraine until President Volodymyr Zelenskyy agreed to announce investigations involving Trump's political opponents.
The stakes are high for all players, with the 2020 elections less than a year away.
The scandal exploded in September after a US intelligence community whistle-blower filed a confidential internal complaint that came to light when the White House tried to block Congress from seeing it.
The US president has denied there was any quid pro quo (Latin for "favour for a favour") in his dealings with Zelenskyy and the White House released a summary of the July 25 phone between the US and Ukrainian leaders that Trump claims was a "perfect" conversation.
In the call, Trump pushes Zelenskyy to open an investigation into former Vice President Joe Biden, a top 2020 Democratic presidential contender, and his son, Hunter, who had served on the board of a Ukrainian gas company. There has been no evidence of any wrongdoing by the Bidens.
Just weeks before the call, Trump ordered his administration to freeze nearly $400m in military aid to Ukraine. The money was eventually released.
Since the launch of the inquiry, the House Intelligence Committee and the Oversight and Foreign Affairs committees have jointly called witnesses behind closed doors. According to transcripts of their testimony, current and former US officials have described what appears to be a campaign to pressure Ukraine into agreeing to launch the investigation.
Wednesday's hearings will take place in a live, televised format.
Taylor stepped in to serve as the diplomat in Ukraine after Trump recalled Marie Yovanovitch, who was serving as ambassador to the Eastern European country. Yovanovitch is scheduled to testify on Friday.
"Collectively these three diplomats bring decades of dedicated and exemplary service to our nation, and I believe it is vitally important that the American people and all members of Congress hear in their own words what they experienced and witnessed," Intelligence Committee Chairman Adam Schiff wrote in a letter to colleagues on Tuesday.
Several additional witnesses have been scheduled for public hearings next week. A request by Republicans to call Hunter Biden and the whistle-blower to appear before the impeachment hearings was refused by Schiff.-Al Jazeera