Shanahan Withdraws as Defense Secretary Nominee

President Trump on Tuesday pulled the nomination of Patrick M. Shanahan to be the permanent defense secretary, saying on Twitter that Mr. Shanahan would devote more time to his family.

The move leaves the Pentagon without a permanent leader at a time of escalating tensions with Iran after attacks on oil tankers in the Persian Gulf. The Trump administration has blamed Iran for the explosions that damaged the two tankers.

Mr. Trump named Mark T. Esper, the secretary of the Army and a former Raytheon executive, to take over as acting secretary of defense. 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 defense secretary. But it is the president’s prerogative to withdraw the nomination.

“I would welcome the opportunity to be secretary of defense, but not at the expense of being a good father,” Mr. Shanahan said in a statement on Tuesday afternoon.

At the Pentagon, officials were internally discussing that a routine F.B.I. investigation for cabinet nominees was dragging on for Mr. Shanahan because of his divorce, which included an allegation from his ex-wife — denied by Mr. Shanahan — that he punched her in the stomach. Mr. Shanahan said that his ex-wife started the fight, and his spokesman said that she was arrested and charged with domestic violence, charges which were eventually dropped.

According to court documents viewed by The New York Times, in 2011 Mr. Shanahan’s son, who was 17 at the time, hit his mother repeatedly with a baseball bat, and she was hospitalized.

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

During his tenure, Mr. Shanahan was criticized for slighting Lockheed Martin, Boeing’s chief competitor, for its mismanagement of the F-35 Joint Strike Fighter, an aircraft that is years behind schedule and millions of dollars over budget.

He was widely viewed as acquiescing to the White House and other government officials, including John R. Bolton, the national security adviser, and Mike Pompeo, the secretary of state. Mr. Shanahan famously said that the Pentagon would not be viewed as the “Department of No.”

Mr. Trump’s decision not to move ahead with Mr. Shanahan is the latest evidence of the difficulty that the president has had in permanently filling the top jobs in his administration.

The president also has an acting chief of staff at the White House and an acting secretary of homeland security.

Mr. Esper, a top lobbyist for Raytheon and an executive at the U.S. Chamber of Commerce, has a long history of ties to lawmakers on Capitol Hill, where he worked as an adviser to Bill Frist, the former Senate majority leader, and various committees with jurisdiction over foreign policy and national security.

Besides Mr. Esper, officials said that Mike Pompeo, the secretary of state, and Richard V. Spencer, the secretary of the Navy, are on the short list for defense secretary.

This is a developing story. It will be updated.