WASHINGTON (NYTIMES) - United States President Donald Trump on Tuesday (June 18) withdrew the nomination of Mr Patrick M. Shanahan to be the permanent defence secretary, leaving the Pentagon in transition at a time of escalating tensions with Iran and questions about the role of the military at the border with Mexico.

Mr Shanahan, who had been serving as the acting defence secretary, announced his resignation as a routine FBI background investigation, conducted on all Cabinet nominees, was continuing because of his divorce.

Mr Shanahan's former wife had accused him of punching her in the stomach, which he has denied. He said his former wife started the fight, and his spokesman said she was arrested and charged with domestic violence, charges which were eventually dropped.

Mr Trump named Mr Mark T. Esper, secretary of the Army and a former Raytheon executive, to take over as acting secretary of defence. He did not say whether Mr Esper would be nominated for the permanent position.

In a Twitter post, the President said the withdrawal was the decision of Mr Shanahan, who has served for six months as acting defence secretary. But it is the President's prerogative to withdraw the nomination.

According to court documents viewed by The New York Times, in 2011, Mr Shanahan's son, who was 17 at the time, reportedly hit his mother with a baseball bat, and she was hospitalised. The next day, Mr Shanahan flew from Seattle to Florida and stayed with his son in a hotel room for several days before his son turned himself in to the authorities.

"I would welcome the opportunity to be secretary of defence, but not at the expense of being a good father," Mr Shanahan said on Tuesday afternoon.

In an interview with The Washington Post published Tuesday, Mr Shanahan said "bad things can happen to good families". He called the episode "a tragedy" and said dredging it up publicly "will ruin my son's life".

Mr Esper, a top lobbyist for Raytheon and an executive at the US Chamber of Commerce, has a long history of ties to lawmakers on Capitol Hill.

Besides Mr Esper, who was confirmed as secretary of the Army in November 2017, officials said Mr Mike Pompeo, secretary of state, and Mr Richard V. Spencer, secretary of the Navy, are on the shortlist for defence secretary.

During his six-month tenure as the department's acting secretary, Mr Shanahan was widely viewed as acquiescing to the White House and other administration officials, including national security adviser John Bolton and Mr Pompeo.

Mr Shanahan famously said that the Pentagon would not be viewed as the "Department of No".