WASHINGTON — After months of delay, President Donald Trump is expected Monday to ask the Senate to confirm Mark Esper as the successor to former Defense Secretary Jim Mattis, whose resignation opened an unprecedented period of senior-level instability at the Pentagon.
Esper's nomination has been in the works for weeks and he is already serving as the acting secretary. In a twist, he would have to step aside from his temporary post leading the Pentagon while the Senate considers his nomination for the permanent job.
A third fill-in will be named, this time Richard Spencer, who has served as the civilian leader of the Navy since August 2017.
His tenure as acting secretary is expected to be brief. Esper is expected to be confirmed as early as Thursday and then sworn in as the permanent secretary. Spencer would then return to the Navy.
The Republican-led Senate will hold a confirmation hearing for Esper on Tuesday.
Esper took over as acting secretary in June when Patrick Shanahan abruptly quit after having served as acting secretary since Mattis departed.
Prior to the Trump administration, only twice before has the Defense Department been led by an acting secretary — most recently in 1989 — and never has it had more than one in a single year.
The lack of stable leadership atop the Pentagon has raised questions in Congress at a time of heightened tensions with Iran and continued U.S. wars in Afghanistan and Syria.
Mattis resigned after two years in the job after a series of policy disagreements with Trump, climaxing with Trump's since-rescinded decision to pull all U.S. troops out of Syria. When Mattis left, Shanahan moved up from being deputy defense secretary, but Trump never nominated Shanahan for the top spot.
There also is no Senate-confirmed deputy secretary of defense or civilian leader of the Air Force. The vice chairman of the Joint Chiefs of Staff, Gen. Paul Selva, is scheduled to retire July 31, and his nominated successor, Gen. John Hyten, has yet to be scheduled for a Senate confirmation hearing.
A military officer has accused Hyten of sexual misconduct. An investigation found insufficient evidence to charge Hyten, but some members of Congress have raised questions about that process.
It's unclear whether Hyten's nomination will proceed.
Esper, who has been the civilian leader of the Army since November 2017, has a wide range of experience with defense issues, including years on Capitol Hill. More recently he was a lobbyist for Raytheon Co., which does a lot of business with the Pentagon.
Esper's former work with Raytheon is likely to come up at his Senate Armed Services Committee hearing on Tuesday. Sen. Elizabeth Warren, a candidate for the Democratic presidential nomination and a member of the committee, has raised questions about Esper's lobbying background.