Trump's acting Pentagon chief abruptly resigns after FBI investigation delays his Senate confirmation hearing

President Donald Trump's acting defense secretary abruptly resigned after an FBI investigation further delayed his confirmation hearings.

Patrick Shanahan has headed the Department of Defense since January, after James Mattis resigned, but the Pentagon has been fielding questions from the media about his personal life -- including accusations of abuse from his ex-wife, who was also arrested as part of a domestic dispute.

"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.

"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!"