During the Poland trip, Matthews was also in a meeting between Zelensky and Vice President Mike Pence, who was filling in for Trump after the president called off his trip to monitor potential hurricane damages in the U.S.

Still, Matthews has not been pulled into the Democrats’ impeachment probe, according to an administration official.

"Mr. Matthews is a dedicated public servant who did an exceptional job implementing the president’s policies while at the National Security Council," said an NSC spokesperson. "We have no doubt he will continue to serve his country well in his future endeavors."

Matthews' departure from the NSC further culls the shrinking team that has seen considerable turnover since Bolton left his post in September. Morrison, the top NSC Russia official, left his post on the eve of his testimony before congressional impeachment investigators.

There is no replacement in line for Matthews, said the official, an increasing trend since new national security advisor Robert O’Brien expressed a desire to trim the NSC. It’s unclear what Matthews plans are after he leaves his role. An administration official only confirmed that the U.S. Army did not extend Matthews’ rotation with the White House.

Matthews joined the NSC in 2018 from the Department of Defense, where he served as a senior attorney for the Department of the Army. In 2016, he was a member of the Trump transition’s Defense Department landing team.

Last year Matthews, a Harvard Law graduate, was promoted to the rank of colonel in the District of Columbia National Guard.

During a 2017 Black History Month Listening Session at the White House with President Trump, Matthews introduced himself as “a veteran and a longtime supporter” of the president.

Daniel Lippman contributed to this report.