Michael McKinley, Pompeo's former senior adviser, testifies before impeachment committees

Secretary of State Mike Pompeo’s former senior adviser who resigned last week testified before three House committees leading the impeachment probe of President Donald Trump.

Michael McKinley, a veteran diplomat who served as U.S. ambassador to Brazil, Afghanistan, Colombia, and Peru, is the sixth witness called by the House Intelligence, Oversight, and Foreign Affairs committees as they investigate Trump and his personal lawyer Rudy Giuliani’s effort to pressure Ukraine to open corruption investigations for Trump’s political benefit.

McKinley departed the State Department Friday amid frustration and anger over how State Department rank and file have been treated during the Trump administration.

McKinley, who left Capitol Hill Wednesday afternoon, told House impeachment investigators he decided to leave the State Department over the treatment of former U.S. Ambassador to Ukraine Marie Yovanovitch, according to a source familiar with his testimony.

He testified that he asked Pompeo to show support for Yovanovitch, but that the secretary of state didn't respond, according to the source.

It is unclear if McKinley was subpoenaed or showed up willingly. The State Department has ordered active officials not to appear before the committees, but two other former U.S officials have not been blocked from testifying: special envoy for Ukraine Kurt Volker, who resigned after it was revealed how he facilitated Giuliani’s effort, and Fiona Hill, the senior Russia official on Trump’s National Security Council who departed days before Trump’s controversial call with Ukraine’s new president Volodymyr Zelenskiy.

Volker appeared on Capitol Hill Wednesday as well to review the transcript of his closed door interview on Oct. 3, according to Rep. Mark Meadows, R-N.C., and other sources familiar with his appearance. Volker, who did not answer any questions from reporters as he entered a secure room for classified testimony, has been a key witness in the impeachment inquiry after handing over text messages that show he and Sondland pushing Zelenskiy and his aides to announce new investigations in order to secure a meeting with Trump.

Two current State Department officials were subpoenaed and complied, defying their order not to appear: Yovanovitch and Deputy Assistant Secretary of State George Kent, whose portfolio includes Ukraine and other Eastern European countries. Gordon Sondland, the U.S. ambassador to the European Union, will comply with a subpoena and testify Thursday after not showing up last Tuesday.

The treatment of Yovanovitch has been particularly galling to career diplomats. She has served under Republican and Democrat administrations and was nominated to be ambassador to Bulgaria by George W. Bush and ambassador to Ukraine by Barack Obama. But she has been smeared by Giuliani, his associates, and a corrupt Ukrainian prosecutor general who has since recanted his allegations. After months of allegations of corruption and obstruction that the State Department called an "outright fabrication," Yovanovitch was recalled early from her post in Kyiv by Trump, who later called her "bad news" to Zelenskiy.

McKinley stepped down as Pompeo’s senior adviser Friday after serving as a key conduit to the Foreign Service, the U.S. diplomatic corps. In a farewell note to colleagues, McKinley cited personal reasons and said it was time to move on after 37 years, but he was reportedly concerned the mistreatment of colleagues. Beyond Yovanovitch's firing, career diplomats have been upset by political retaliations against officials detailed by the State Department's inspector general and penalties against former and current officials who emailed Hillary Clinton's private email address.

As a close adviser, McKinley traveled often with Pompeo during Pompeo's year and a half as secretary of state, returning to Washington from Brasilia just weeks after Pompeo was sworn in to join his inner circle. His guidance was important to Pompeo who worked to restore trust among career diplomats after his predecessor Rex Tillerson was seen as destroying their ranks with budget cuts, a costly, unpopular department redesign, and a freeze on hiring family members to work at missions overseas.

But it’s unclear how much McKinley knew about Giuliani’s efforts and how they were aided by Sondland and Volker, the department’s attempts to dispel a smear campaign against Yovanovitch by Giuliani and his associates, or the hold on $392 million of security assistance to Ukraine from the State Department and Pentagon.

McKinkey is not included in internal emails given to Congress by the State Department inspector general and obtained by ABC News, where officials like Kent are seen countering a “fake news driven smear” campaign against Yovanovitch. But other senior advisers to Pompeo are included, including Under Secretary for Political Affairs David Hale, another well-respected ambassador and the department’s highest-ranking career Foreign Service officer, as well as State Department counselor Ulrich Brechbuhl, a West Point classmate and longtime friend of Pompeo.

ABC News's Katherine Faulders and Ben Siegel contributed to this report from Capitol Hill.