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, said Republicans must justify the relevance of witnesses they want to call in public hearings as part of the impeachment inquiry into 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.

Schiff in a letter to Rep. Devin Nunes Devin Gerald NunesOvernight Defense: Stopgap spending measure awaits Senate vote | Trump nominates former Nunes aide for intelligence community watchdog | Trump extends ban on racial discrimination training to contractors, military Trump nominates former Nunes aide to serve as intel community inspector general Sunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election MORE (R-Calif.), the ranking member of the panel, late Wednesday outlined questions that will be used to weigh whether a witness's testimony would be germane.

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Among the questions are whether President Trump requested “that a foreign leader and government initiate investigations to benefit the President’s personal political interests” and if he sought to use his office “to apply pressure on the head of state and government of Ukraine to advance the President’s personal political interests,” including leveraging an Oval Office meeting or millions of dollars in military aid.

Schiff also said witnesses must speak to whether the president or administration officials sought to obstruct or cover up any evidence regarding Trump’s actions.

Republicans must submit their witness requests to Schiff by Saturday, including a written justification for the relevance of the testimony from each person they intend to call.

House Democrats announced Wednesday that they will hold their first public impeachment hearings next week as they ramp up their investigation into Trump's dealings with Ukraine.

Schiff said that William Taylor, the top U.S. diplomat to Ukraine, and George Kent, a top State Department official, will testify on Wednesday. Former U.S. Ambassador to Ukraine Marie Yovanovitch is then expected to testify on Nov. 15.

Democrats and Republicans on the House Intelligence, Oversight and Reform, and Foreign Affairs committees have already conducted several interviews behind closed doors.

Schiff said in the letter to Nunes that Democrats don’t intend to request public testimony from every witness the committees have already interviewed, and Rep. Mark Meadows Mark Randall MeadowsWhite House chief of staff knocks FBI director over testimony on election fraud Anxious Democrats amp up pressure for vote on COVID-19 aid Pelosi hopeful COVID-19 relief talks resume 'soon' MORE (R-N.C.) has said the GOP would likely seek testimony from people beyond those who have already spoken privately.

Rep. Jim Jordan James (Jim) Daniel JordanHouse panel pulls Powell into partisan battles over pandemic Sunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election House passes resolution condemning anti-Asian discrimination relating to coronavirus MORE (R-Ohio) added Thursday that Republicans intend to subpoena the government whistleblower who first raised alarm about interactions between Trump and Ukrainian President Volodymyr Zelensky. The effort is likely to fail, however, as Democrats have said they do not intend to out the anonymous figure over safety concerns and that other witnesses have already gone beyond what the official alleged.

The House’s impeachment inquiry was launched in September amid Democratic concerns that Trump leveraged $400 million in military aid to pressure Zelensky to open an investigation into unfounded corruption allegations against 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, a top candidate for the Democratic presidential nomination, and Biden's son.

The White House has repeatedly blasted the House investigation as a "witch hunt" and decried Democrats' efforts as "unhinged" after they voted to formalize the inquiry last week.

Democrats have countered the president has abused his oath of office by seeking to involve foreign nations in U.S. domestic politics after publicizing testimony from several witnesses saying there was a quid pro quo surrounding Trump's dealings with Ukraine.