Former National Security Adviser John Bolton was voicing concerns about Rudy Giuliani's influence over Ukraine policy prior to President Trump's infamous July phone call, a State Department official is set to testify.

Christopher Anderson, the former assistant to former special envoy for Ukraine Kurt Volker, will testify Wednesday that Bolton in a June meeting with U.S. officials said he "supported increased senior White House engagement" with Ukraine, but he "cautioned that Mr. Giuliani was a key voice with the President on Ukraine which could be an obstacle to increased White House engagement," CNN and The Wall Street Journal report.

This meeting took place the month prior to the phone call between Trump and Ukrainian President Volodymyr Zelensky, on which Trump pushed for investigations that he thought might help him politically, including into former Vice President Joe Biden and his son. Congress in its impeachment inquiry is investigating whether Trump abused the power of his presidency by conditioning aid to Ukraine on the opening of these investigations.

Previous witnesses in the impeachment inquiry have testified about the unusual role Giuliani, Trump's personal lawyer, played in Ukraine policy, with diplomat Gordon Sondland testifying he was "disappointed" when the president directed officials to talk with Giuliani about Ukraine matters while he was trying to arrange a meeting between Trump and Zelensky, saying he felt he had no choice but to do so if he wanted to get this meeting set up. Sondland also said he "did not understand, until much later, that Mr. Giuliani's agenda might have also included an effort to prompt the Ukrainians to investigate Vice President Biden or his son."

Anderson is also the latest impeachment witness to testify about Bolton's apparent Giuliani concerns, with former Russia adviser Fiona Hill reportedly testifying that Bolton compared Giuliani to "a hand grenade who's going to blow everybody up." Giuliani shot back by saying Bolton "is described by many as an atomic bomb." Brendan Morrow