Democratic presidential hopefuls Sen. Amy Klobuchar Amy Klobuchar3 reasons why Biden is misreading the politics of court packing Social media platforms put muscle into National Voter Registration Day Battle lines drawn on precedent in Supreme Court fight MORE (D-Minn.) and businessman Tom Steyer Tom SteyerTV ads favored Biden 2-1 in past month Inslee calls Biden climate plan 'perfect for the moment' OVERNIGHT ENERGY: Trump administration finalizes plan to open up Alaska wildlife refuge to drilling | California finalizes fuel efficiency deal with five automakers, undercutting Trump | Democrats use vulnerable GOP senators to get rare win on environment MORE during Thursday's Democratic primary debate called on White House officials to testify during the Senate's impeachment trial.

"As we face this trial in the Senate, if the president claims that he is so innocent, then why doesn’t he have all the president’s men testify?" Klobuchar told the audience at the PBS News Hour/Politico debate in Los Angeles.

"Richard Nixon had his top people testify," she continued. "We should be hearing from [White House chief of staff Mick] Mulvaney, who is the one under oath. Witnesses have said that Mulvaney is the one that said. 'Okay, we're going to withhold this aid to a fledgling democracy to get dirt on a political opponent.'"

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"We should hear from [former National Security Adviser John] Bolton, who told his own staff to go see a lawyer after they met with the president. That is the case," she said.

Steyer echoed Klobuchar's sentiment, saying witnesses are required to present a fair case to the American people.

"I actually agree with Senator Klobuchar," Steyer said. "The question here is if we want the American people to understand what is going on, we need to have the administration officials testify on TV so we can judge. The court that counts is the court of public of opinion."

Klobuchar's comments come after Senate Minority Leader Charles Schumer Chuck SchumerPelosi: Trump Supreme Court pick 'threatens' Affordable Care Act Will Democrats attempt to pack the Supreme Court again? Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' MORE (D-N.Y.) said on Wednesday that he will ask for votes during the impeachment trial calling for witnesses, including Bolton and Mulvaney, to testify.

Schumer has also said he would like Mulvaney's senior adviser Robert Blair and budget staffer Michael Duffey to testify.

However, Republican senators have suggested that they want to delay a decision on witnesses until after the trial has started.

Schumer on Thursday met with Senator Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellHawley warns Schumer to steer clear of Catholic-based criticisms of Barrett Senate GOP set to vote on Trump's Supreme Court pick before election Harris slams Trump's Supreme Court pick as an attempt to 'destroy the Affordable Care Act' MORE (R-Ky.), but the two did not come to an agreement on witnesses or requests for additional documents ahead of the Christmas break.