By tapping former Boeing executive Patrick Shanahan to temporarily replace famed former Marine Gen. James Mattis as secretary of defense, President Trump may have found a like-minded advocate for the U.S. weapons industry.

Shanahan is a controversial choice. During Shanahan's two-year stint as Mattis's deputy defense secretary, Boeing has landed a series of lucrative military contracts worth $20 billion, on top of the Chicago company's previous deal to build aerial-refueling tankers and naval fighters for the Pentagon.

Mattis' resignation on Thursday came one day after Trump announced, via Twitter, that the terror group known as Islamic State is no longer a threat and the United States will withdraw all 2,000 of its troops from Syria.

Trump reportedly made his decision to quit Syria during a Dec. 14 phone call with Turkish president Recep Tayyip Erdogan, who is eager to attack Kurdish groups in northern Syria who are strong allies of the United States. “You know what? It’s yours,” Trump reportedly said of Syria. He had a similar call with Erdogan on Sunday.

On Friday, Trump continued his America First policy, ordering the Pentagon to withdraw 7,000 troops from Afghanistan, a move that could open the door to mercenary firms to take over the U.S. war effort despite Afghan governnment opposition.

Lt. Col. Joe Buccino, a spokesperson for Shanahan, sent the following statement to the Daily Beast: “Mr. Shanahan is recused from any DoD decisions impacting Boeing, and the Department’s legal advisors have a screening process to ensure that Boeing-related issues are not routed to Mr. Shanahan. While the details of the Department’s FY2020 budget request remain pre-decisional, the screening process was in place throughout the budget review to ensure that any DoD programmatic decisions impacting Boeing were neither made nor influenced by Mr. Shanahan.”

Experts have warned that Islamic State is rebuilding in the Middle East. The Taliban likewise have gained strength in recent months. A U.S. pullout in Afghanistan could undermine peace talks with the Taliban. “I believe the Taliban will see this as a reason to stall,” said Bill Roggio, an Afghanistan analyst with the Foundation for Defense of Democracies in Washington, D.C.

In his resignation letter, Mattis rebuked Trump for his flippant treatment of America's allies. “My views on treating allies with respect and also being clear-eyed about both malign actors and strategic competitors are strongly held,” Mattis wrote, adding that he would stay on until February to help with a smooth transition.

On Sunday, Trump tweeted that Mattis would step down before Jan. 1 and Shanahan would become acting defense secretary.

It's unclear whether Shanahan would urge Trump to be more respectful of America's alliances. But Shanahan's statements on ISIS, during his confirmation, seem to contradict Trump's own position.

“I would consider success in defeating ISIS to be when the threat the group poses has been degraded to a point where it is localized and periodic and when it can be addressed as a law-enforcement issue by partner nations and forces without extensive assistance from the United States,” Shanahan said.

But in Shanahan, he does have someone who is likely to share his interest in business. Trump has ordered diplomats to prioritize foreign sales of American-made arms. “Patrick has a long list of accomplishments while serving as Deputy, & previously Boeing,” Trump tweeted. “He will be great!”

Shanahan said during his 2017 Senate confirmation hearing that technology, not strategy, is his expertise.

“ I believe my skill set strongly complements that of Secretary Mattis.He is a master strategist with deep military and foreign policy experience...I bring strong execution skills with background in technology development and business management. ” — Deputy Secretary of Defense Patrick Shanahan

"I believe my skill set strongly complements that of Secretary Mattis," Shanahan said. "He is a master strategist with deep military and foreign policy experience. As deputy secretary of defense and Secretary Mattis’ chief operating officer, I bring strong execution skills with background in technology development and business management."

Pentagon ethics rules require Shanahan to recuse himself from any decisions regarding Boeing. But the plane-maker, which historically places second behind Lockheed Martin as America's biggest defense contractor, has enjoyed a chain of successes winning major competitive contracts.

In August, Boeing snagged a $7-billion contract to build aerial-refueling drones for the Navy. A month later it won a $2.4-billion contract to build helicopters for the Air Force. In September, it also scored a $9-billion contract to build training jets for the flying branch.

A much smaller contract perhaps is the most troubling. On Dec. 21, Bloomberg reported that the Pentagon would request funding in the 2020 defense budget for a dozen upgraded F-15X fighters worth $1.2 billion. Boeing builds the 1970s-vintage, non-stealthy F-15 at its plant in St. Louis.

The Air Force for years has said it does not want more F-15s, instead preferring to order F-35 stealth fighters from Lockheed for around the same price as the F-15X, per plane. But the Pentagon reportedly overruled the Air Force and added the new Boeing fighters to the budget.

Shanahan "prodded" planners to include the planes, according to Bloomberg—this despite the requirement that Shanahan recuse himself from decisions involving Boeing.

Several member of Trump's cabinet have been accused of using their positions to benefit allies in U.S. industry. Former interior secretary Ryan Zinke resigned on Dec. 15 amid a flurry of ethics investigations, including one into a Montana land deal that involved an organization run by Zinke's wife.