WASHINGTON (AP) - A senior career foreign service officer who served as a top adviser to Secretary of State Mike Pompeo has resigned, adding to the tumult in the State Department over the Trump administration’s handling of Ukraine and the treatment of diplomats.

Pompeo’s de facto chief of staff, Michael McKinley, announced his retirement after a nearly four-decade career as a diplomat.

“The decision is personal,” McKinley wrote in a farewell email. “It’s time after 37 years with the department.”

He did not mention the Ukraine situation that is now at the center of an impeachment probe.

McKinley’s resignation took effect Friday, the same day former U.S. ambassador to Ukraine Marie Yovanovitch, another career foreign service officer, told congressional investigators that she had been removed from her post due to political pressure from the White House and lamented the politicization of the diplomatic corps.

The ousting of Yovanovitch was cited in a whistleblower’s report that sparked the impeachment inquiry in Congress looking into whether President Donald Trump pressed the president of Ukraine to investigate a political rival while his administration was delaying military aid to the Eastern European country.

McKinley, 65, is a four-time time ambassador, having served as the top U.S. envoy to Peru, Colombia, Afghanistan and most recently Brazil. Pompeo pulled McKinley from Brazil to be his senior adviser as part of a push to put more career employees into senior positions after his predecessor Rex Tillerson was faulted for sidelining them.

Pompeo has been criticized, however, for failing to publicly defend Yovanovitch from a campaign by supporters of President Donald Trump to oust her. Yovanovitch told congressional investigators on Friday that her treatment had a chilling effect on other career diplomats who she said had previously been able to count on support from whatever administration they served.

In an interview on Friday in Nashville with The Tennessean newspaper, Pompeo denied that he had not sufficiently protected his staff.

“I protect every single State Department employee,” he said, repeating complaints that the congressional inquiry is not fair. “We have and we will continue to stand up. When the State Department employees are doing things right, when they’re behaving in ways that are consistent with the rule of law and working on President Trump’s and America’s mission, I’ll always stand with them; I’ll always have their back.”

Although Pompeo has pushed to place more career diplomats in top positions, many posts remain vacant, and already poor morale at the State Department has been made worse by revelations about how Yovanovitch was treated.

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