Patrick Shanahan and Donald Trump / REUTERS

U.S. President Donald Trump has appointed Mark Esper as new Acting Secretary of Defense.

"Acting Secretary of Defense Patrick Shanahan, who has done a wonderful job, has decided not to go forward with his confirmation process so that he can devote more time to his family," Trump tweeted on Tuesday.

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"I thank Pat for his outstanding service and will be naming Secretary of the Army, Mark Esper, to be the new Acting Secretary of Defense. I know Mark, and have no doubt he will do a fantastic job!" he added.

Shanahan had held his post since January 1, 2019. It became known early in May 2019 that Trump planned to appoint him as U.S. Secretary of Defense.