House Intelligence Committee Chairman Adam Schiff said Wednesday public hearings in the impeachment investigation will begin next week with three State Department employees who provided key testimony during closed-door questioning.

The announcement comes less than a week after the House approved rules governing the hearings into whether President Trump abused his office by pressuring Ukraine to dig up dirt on his political opponents. He has decried the impeachment investigation as a sham, a scam, a hoax and a witch hunt, insisting he has done nothing wrong.

The announcement came as investigators questioned David Hale, the third-ranking official at the State Department, and follows this week’s release of four transcripts of closed-door testimony by witnesses. Democrats say Hale can provide information on why U.S. Ambassador to Ukraine Marie Yovanovitch was ousted.

 “We will begin our open hearings in the impeachment inquiry next week,” Schiff, D-Calif., who is leading the investigation, told reporters. “We will begin with Ambassador [William] Taylor and Ambassador [George] Kent on Wednesday and we will have Ambassador Yovanovitch on Friday.”

Taylor, a Vietnam War veteran, was George W. Bush’s ambassador to Ukraine and currently is the acting ambassador to Kyiv. Kent is the deputy assistant secretary of state.

All three witnesses have testified behind closed doors. Yovanovitch’s testimony was released Monday. During his testimony, Taylor said the administration tried to pressure Ukraine to commit to investigating Democrats for Trump’s political benefit. His deposition was to be released later Wednesday.

Republicans have been clamoring for an open investigation but have criticized House rules governing the process. Each side will be able to tap trained staff to conduct the witness questioning for as long as 45 minutes at a time.

Meanwhile, Sen. Rand Paul, R-Ky., threatened to release the name of the whistleblower whose complaint about Trump’s July 25 call to Ukraine President Volodymyr Zelenski touched off the impeachment inquiry.

"I'm more than willing to, and I probably will at some point. ... There is no law preventing anybody from saying the name," Paul told reporters.

He later said on Fox News he hasn’t done it yet, even though he’s pretty sure he knows who it is, because he wants the focus on the impeachment process itself. Paul alleged the whistleblower used to work for former Vice President Joe Biden and urged the media to “print his name” during a rally Monday night in Kentucky.

Democrats contend the whistleblower is protected by law from exposure.