GOP counsel Steve Castor acknowledged what both he and William Taylor, the chargé d’affaires for Ukraine, described as an “irregular channel” of policymaking between the U.S. and Ukraine during his line of questioning at Wednesday's public impeachment hearing.

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Castor asked Taylor, a career diplomat, why he did not “wrest control” away from the back-channel efforts that had been led by 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, the president's personal attorney.

Those back-channel efforts are a key focus of the impeachment inquiry led by House Democrats, who are seeking to build a case that Trump withheld assistance to Ukraine to get its leadership to conduct investigations of 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 his son.

Taylor responded that he chose not to because the “regular” and “irregular” channels were both “going in the same direction” in terms of prioritizing a meeting between 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 Ukrainian President Volodymyr Zelensky.

He explained that he initially thought the meeting was being held up until Ukraine publicly announced investigations of the Bidens but that he later learned security assistance was also being held up.

During his opening statement on Wednesday, Taylor described an “informal channel” that included Giuliani, former U.S. special envoy to Ukraine Kurt Volker Kurt VolkerGOP senators request details on Hunter Biden's travel for probe Yovanovitch retires from State Department: reports Live coverage: Senators enter second day of questions in impeachment trial MORE, U.S. Ambassador to the European Union Gordon Sondland, Secretary of Energy Rick Perry and acting White House chief of staff Mick Mulvaney. This was opposed to the “regular channel,” which, according to Taylor, involved “formal diplomatic processes.”

Castor continued to refer to the policymaking involving Volker, Sondland, Giuliani and others as the “irregular channel,” including when questioning Taylor on whether he had had any contact with Giuliani as part of “irregular channel business” and whether Taylor had raised concerns about this policymaking channel.

Castor asked Taylor about whether it was "outlandish" for Sondland to be involved in Ukrainian policymaking, and Taylor said it was "unusual."

Castor commented in response that "it may be irregular, but it's certainly not outlandish."

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