Christopher Anderson, former assistant to special envoy to the Ukraine Kurt Volker, will testify Wednesday that former NSA John Bolton warned about Rudy Giuliani’s influence on the President with regards to Ukrainian policy.

According to his prepared remarks obtained by CNN, Anderson will say that during a meeting in mid-June, Bolton drew his attention to the unofficial backchannel actually running U.S.-Ukraine relations.

“He cautioned that Mr. Giuliani was a key voice with the President on Ukraine which could be an obstacle to increased White House engagement,” Anderson is expected to relate of his conversation with Bolton.

Anderson is also expected to detail an episode where the White House blocked a statement condemning Russian aggression towards Ukraine.

In addition to Anderson, his successor, Catherine Croft, is slated to speak Wednesday.

According to her prepared remarks, she will tell of a lobbyist’s attempts to oust former US Ambassador to the Ukraine Marie Yovanovitch, an effort spearheaded by Giuliani when Yovanovitch was not being receptive to the pressure campaign.

She will also relate her experience being on a video call when an Office of Management and Budget official said that acting director and acting chief of staff Mick Mulvaney put an “informal hold” on military aid to Ukraine at the President’s direction.