WASHINGTON >> President Donald Trump plans to nominate Army Secretary Mark Esper for defense secretary following the messy withdrawal of the president’s previous choice, acting Secretary Patrick Shanahan.

The White House made the announcement tonight.

Esper was already set to take over from Shanahan as acting secretary, at 12:01 a.m. EDT Monday, amid heightened tensions between the U.S. and Iran. He faces a vetting and Senate confirmation process that could drag on for weeks if not months. He is scheduled to attend a NATO defense ministers meeting in Brussels next week.

Trump signaled his intentions Tuesday as he announced Shanahan’s departure, saying he would “most likely” nominate Esper as defense secretary and that he could win Senate confirmation “very quickly” because he’s “very experienced.”

Esper, 55, served as an aide to former Sen. Bill Frist, a Tennessee Republican, giving him a foundation of experience and relationships on Capitol Hill. He also was an executive with Raytheon Co., which United Technologies Corp. now plans to buy to create an aerospace and defense giant with $74 billion in sales.

Like Shanahan, a former Boeing Co. vice president, Esper would be expected to recuse himself from decisions on contracts involving his former employer.

The turmoil at the Defense Department comes as Trump said today he had called off retaliatory strikes on three Iranian sites following the shooting down of a U.S. Navy drone, saying the action would not have been “proportionate.” Airstrikes would have raised the specter of a far broader conflict in the volatile region, which supplies one-third of the world’s oil.

Shanahan had been serving in an acting role since former Defense Secretary Jim Mattis resigned in December. But Shanahan took his name out of consideration to formally replace Mattis after reports about domestic violence episodes in his family. Trump, who never sent Shanahan’s nomination to the Senate, later told reporters he learned about the incidents involving Shanahan and his family only on Monday.

Lawmakers have questioned how conflicting allegations of domestic violence between Shanahan and his former wife took so long to surface and weren’t revealed when he was vetted by the White House and the FBI before his confirmation as deputy defense secretary.

The Senate Armed Services Committee recommended Shanahan as deputy secretary and the full Senate confirmed him on a 92-7 vote in 2017.

Despite bipartisan criticism in Congress that Trump lacks a Senate-confirmed defense secretary — a concern heightened by the tensions with Iran — Esper is likely to face added scrutiny because of concerns over the vetting of Shananan.

Esper, who attended the United States Military Academy at West Point, was in the same class as Secretary of State Michael Pompeo. After graduation, he spent more than a decade on active duty in the Army.

The White House also said tonight that Trump intended to nominate David Norquist to be the Pentagon’s deputy secretary. Norquist has been the Defense Department’s undersecretary and comptroller.