The White House announced Friday that President Trump intends to nominate Army Secretary Mark T. Esper to serve as his secretary of defense as the Pentagon faces a leadership vacuum amid a mounting confrontation with Iran. 

The decision comes as lawmakers increasingly pressure the president to bring stable civilian leadership to the Pentagon, where it has been absent since Jim Mattis abruptly resigned as defense secretary late last year.

The need for a confirmed defense secretary became more pronounced Thursday, as Trump considered a military strike on Iran in retaliation for the downing of a U.S. reconnaissance drone but ultimately backed down over what he said was his concern about Iranian casualties. 

Esper, after studying in the same U.S. Military Academy class as Secretary of State Mike Pompeo, began a long career as an Army infantryman that included serving in the 1991 Persian Gulf War. He later became a Washington insider, honing his defense policy skills as an adviser to Republican lawmakers, a top civilian Pentagon official, a top official at a conservative think tank, a lobbyist for defense contractor Raytheon and most recently the top civilian overseeing the U.S. Army.

His deep understanding of Washington’s inner workings marks a stark contrast to the background of acting defense secretary Patrick Shanahan, who joined the Pentagon after decades of working in the private sector at Boeing and entered government without a military background or the long-standing relationships typical of high-level Defense Department officials.

News of Trump’s intent to nominate Esper was first reported by the New York Times. The White House also announced Friday evening that Trump will nominate Army undersecretary Ryan McCarthy to replace Esper. Trump will also nominate David Norquist, the Defense Department’s chief financial officer, to be the agency’s deputy secretary.

Trump intended to nominate Shanahan to run the Pentagon, but the former Boeing executive withdrew from consideration this week as reports surfaced about his contentious divorce, including an incident in 2011 when his son attacked his ex-wife with a baseball bat. Shanahan’s last day is Sunday.

After Shanahan bowed out, Trump tweeted that Esper would be the new acting defense secretary.

He also said Tuesday that he would “most likely” nominate Esper.

Sen. James M. Inhofe (R-Okla.), the chairman of the Senate Armed Services Committee, told reporters that he spoke to Trump on Thursday morning and received word that the president was planning to pick a new defense secretary soon. Inhofe suggested that the president told him Esper was his choice, according to Politico.  Esper, 55, served in the 101st Airborne Division during the Gulf War and later commanded an airborne rifle company in Europe, receiving the Legion of Merit and a Bronze Star, according to his official Army biography. He gained policy experience working for Republican lawmakers on Capitol Hill, including as national security adviser to then-Senate Majority Leader Bill Frist (R-Tenn.) and as policy director for the House Armed Services Committee.

He left government and served as chief of staff at the Heritage Foundation, a conservative think tank, and then in the defense industry, first as the chief operating officer of the Aerospace Industries Association and later as vice president of government relations for the defense contractor Raytheon. He also held positions as executive vice president for the U.S. Chamber of Commerce’s Global Intellectual Property Center and as its vice president for Europe and Eurasian affairs.

Trump’s timeline for nominating Esper is complicated by the Vacancies Reform Act, which states that when a department secretary steps down, the president must nominate a replacement within 210 days.

If he does not, the official acting in the defense secretary role loses the ability to carry out some “nondelegable” duties, said Arnold Punaro, a retired Marine general who has assisted with defense secretary transitions for years. However, those duties have been difficult to define in the past, according to a Congressional Research Service report on the issue.

Under that premise, Trump must nominate a new defense secretary by July 30, as the 210-day clock on Mattis leaving office runs out, Punaro said. 

Federal law states that if Esper becomes the nominee, he will have to step down as acting defense secretary during his confirmation process, probably leaving the role to Navy Secretary Richard V. Spencer, according to a Defense Department memo on secretary succession.

Trump did not face the same time restrictions with Shanahan serving as acting defense secretary because he already had been confirmed as deputy defense secretary and therefore had all of the powers and responsibilities of the Pentagon chief when necessary, Punaro said.

Dan Lamothe contributed to this report.