US President Donald Trump has announced his choice for defence secretary has withdrawn, shaking up the Pentagon at a time of rising Middle East tensions.
He tweeted that Patrick Shanahan has pulled out of consideration “so that he can devote more time to his family”.
Mr Shanahan, who will be replaced by Army Secretary Mark Esper, had not yet been nominated for the cabinet post.
It comes as Mr Shanahan publicly addressed allegations of domestic violence.
Earlier on Tuesday, USA Today reported the FBI was investigating a 2010 incident in which Mr Shanahan and his ex-wife accused each other of assault.
Minutes after Mr Trump’s announcement, the Washington Post published an interview with Mr Shanahan in which he discussed a 2011 incident when his son, then 17, reportedly beat his mother with a baseball bat, fracturing her skull.
In a statement announcing his resignation, Mr Shanahan called it “unfortunate that a painful and deeply personal family situation from long ago is being dredged up and painted in an incomplete and therefore misleading way”.
He said he did not want his three children “to relive a traumatic chapter in our family’s life and reopen wounds we have worked years to heal”.
Mr Shanahan added: “I would welcome the opportunity to be secretary of defense, but not at the expense of being a good father.”
On Monday, he told the Washington Post that he regretted a legal memo he penned shortly after the alleged attack on his ex-wife.
He wrote that the “use of a baseball bat in self-defence will likely be viewed as an imbalance of force” and that “Will’s mother harassed him for nearly three hours before the incident”.
Before joining the Trump White House, Mr Shanahan had worked as an executive at Boeing, the US aerospace company which holds many US defence department contracts.
He took over six months ago after the resignation of former Defence Secretary James Mattis.
The announcement comes amid renewed tensions between the US and Iran after Washington accused the Islamic republic of attacks last week on two oil tankers in the Gulf of Oman.
Mr Shanahan on Monday announced the deployment of 1,000 US troops to the Middle East to counter “hostile behaviour” by Iranian forces.
He added that the US does “not seek conflict with Iran” and the action had been taken to “ensure the safety and welfare of our military personnel working throughout the region to protect our national interests”