Former senior adviser to Secretary of State Mike Pompeo, Michael McKinley, is expected to detail his concern over the politicization of the State Department during his testimony on Wednesday.

An unnamed source told the Washington Post that McKinley, who resigned last week, will lay out his unease over the removal of Marie Yovanovitch from her post as U.S. ambassador to Ukraine.

“The unwillingness of State Department leadership to defend Yovanovitch or interfere with an obviously partisan effort to intervene in our relationship with Ukraine for the political benefit of the president was too much for him,” the source said.

McKinley will also reportedly discuss with House impeachment inquiry leaders how Trump’s political appointees repeatedly attacked career officials not deemed loyal enough to the President.