Rep. Adam Schiff Adam Bennett SchiffSchiff to subpoena top DHS official, alleges whistleblower deposition is being stonewalled Schiff claims DHS is blocking whistleblower's access to records before testimony GOP lawmakers distance themselves from Trump comments on transfer of power MORE (D-Calif.), the chairman of the House Intelligence Committee, warned Republicans that the panel’s impeachment probe would not be used to investigate former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE or unfounded claims that Ukraine was involved in election meddling in 2016.

“This inquiry is not, and will not serve ... 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 said in a statement.

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The remarks came after House Republicans unveiled a list of witnesses they plan to call before the Intelligence Committee for the impeachment probe. Included in the list are Hunter Biden, the former vice president’s son; the anonymous whistleblower who first raised concerns about President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE’s dealings with Ukraine; and Nellie Ohr, a former Fusion GPS employee who is a top Republican target over their claims she helped produce the Steele dossier.

“The Committee is evaluating the Minority’s witness requests and will give due consideration to witnesses within the scope of the impeachment inquiry, as voted on by the House,” said Schiff.

“As we move into the open hearing phase of the inquiry, the Committee is mindful that we are engaged in a sober endeavor rooted in the Constitution to determine whether the President of the United States engaged in misconduct that warrants impeachment by the House,” he added.

The House’s impeachment inquiry was launched in September amid Democratic concerns that Trump leveraged $400 million in military aid to pressure Ukrainian President Volodymyr Zelensky to publicly open an investigation on unfounded corruption allegations against Joe Biden, a top political rival.

Trump and his Republican allies on Capitol Hill have repeated ungrounded theories that Joe Biden abused his power when as vice president he leaned on a Ukrainian prosecutor to drop an investigation into an energy company on whose board Hunter Biden sat. No evidence suggests that Biden was acting with his son’s interests in mind.

After several witnesses testified behind closed doors in recent weeks that they believed there was a quid pro quo surrounding Trump’s dealings with Ukraine, the impeachment investigation is set to enter a new phase next week when the Intelligence Committee holds the first round of public hearings.

While Republicans have denounced the process so far as not transparent enough, Democrats have aired concerns that the GOP could use the public hearings to derail the investigation and focus on the unfounded claims against Biden.