Deputy Assistant Secretary of State George Kent reportedly raised concerns earlier this year about what he described as pressure from 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 and his lawyer Rudy Giuliani Rudy GiulianiThe Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting CIA found Putin 'probably directing' campaign against Biden: report Democrats fear Russia interference could spoil bid to retake Senate MORE to investigate Trump's political opponents.

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Sources told The New York Times that Kent, who oversees Ukraine policy, expressed concern as far back as March about Giuliani's role in a "disinformation" campaign that aimed to smear people including 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 and then-U.S. Ambassador to Ukraine Marie Yovanovitch.

Kent was deposed on Tuesday as part of the House Democrats' impeachment inquiry.

Democrats are investigating the president following revelations that he pushed Ukraine to investigate the Bidens.

The whistleblower's complaint alleges that White House officials believed Trump was using his office for a political gain during a July 25 call where he pressured Ukraine's leader to investigate Biden, and that officials sought to cover up the call.

Kent's testimony on Tuesday follows last week's testimony from Yovanovitch, who was recalled from her post in May, and former White House aide Fiona Hill.

Olivia Beavers contributed to this story.