In calling the Ukraine whistleblower to testify, Nunes said President Donald Trump "should be afforded an opportunity to confront his accusers." The anonymous whistleblower's account of a telephone call between Trump and Ukrainian president Volodymyr Zelensky set off the impeachment inquiry.

Trump and Republicans have focused on Hunter Biden's role on the board of the Ukrainian gas company, Burisma Holdings, at the same time that his father, Joe Biden, was vice president.

Devon Archer was a longtime business partner of Hunter Biden and served on the board of Burisma alongside him.

Witnesses called to testify who have already given depositions behind closed doors include Kurt Volker, the former special envoy for Ukraine negotiations, Tim Morrison, the Europe and Russia chief for the National Security Council, and David Hale, the undersecretary of State for political affairs.

Volker said in his deposition that he felt compelled to connect Trump's personal lawyer Rudy Giuliani with Ukrainian officials, and that he didn't initially connect the Burisma gas company to the Bidens.

Volker's text messages with Gordon Sondland, U.S. Ambassador to the E.U., and Bill Taylor, a former U.S. ambassador to Ukraine and a longtime Foreign Service officer, were part of explosive evidence that the White House wanted to make elements of the U.S. relationship with Zelensky conditional on Ukraine investigating Trump's domestic political rival.

Alexandra Chalupa, a former DNC staffer who had worked in the White House Office of Public Liaison during the Clinton administration, was also included in the list.

Nellie Ohr, who is married to Justice Department official Bruce Ohr, was also called to testify. Her husband's relationship with former British spy Christopher Steele has been raised repeatedly by Republicans over the infamous dossier on Trump's relationship with Russia.

In response to the release of the list of witnesses, Schiff warned that the the House inquiries would not dive into "sham" investigations or retaliate against the whistleblower.

“This inquiry is not, and will not serve, however, as a vehicle to undertake the same sham investigations into the Bidens or 2016 that the President pressed Ukraine to conduct for his personal political benefit, or to facilitate the President’s effort to threaten, intimidate, and retaliate against the whistleblower who courageously raised the initial alarm," Schiff wrote in a statement.

Schiff also said the committee is evaluating the list and "will give due consideration to witnesses within the scope of the impeachment inquiry, as voted on by the House."

Later Saturday, Trump appeared to respond to the GOP's witness list by adding he would like House Speaker Nancy Pelosi, Schiff, and Joe Biden to appear on the list of witnesses.

"I recommend that Nervous Nancy Pelosi (who backed up Schiff’s lie), Shifty Adam Schiff, Sleepy Joe Biden, the Whistleblower (who miraculously disappeared after I released the transcript of the call), the 2nd Whistleblower (who also disappeared), & the I.G., be part of the list!" Trump tweeted during his flight to attend the Louisiana State University vs. Alabama football game in Tuscaloosa, Alabama.