It hasn’t received much attention, what with Donald Trump suddenly declaring victory against ISIS, ordering U.S. troops out of Syria, and provoking James Mattis to resign in protest.

But the man who is now the president’s principal adviser on the nation’s defense, tasked with leading the largest employer in the world and managing the fallout from Trump’s military retrenchment, has less experience in government (a year and a half) or the military (none) than any defense secretary since an oil magnate served as the acting head of the Pentagon for several weeks during Watergate 45 years ago.

The man’s name is Patrick Shanahan. He’s a relative enigma in American politics. And while he’s only temporarily assuming the top posting at the Defense Department for now, he may be sticking around for a while.

Focus solely on the policy positions Shanahan has staked out, and you’ll hear echoes of his outgoing boss. They’re a reminder of the difficulty Trump will have in finding a new Pentagon chief from any corner of the political-military-industrial complex whose views, as Mattis put it in his resignation letter, “are better aligned” with the president’s. In his disdain for traditional American allies, disregard for the authoritarian threat from Russia and China, and dismissal of the U.S.-led international system as a boondoggle, the commander in chief of the United States’s military largely stands alone.

Read: James Mattis’s final protest against the president

As deputy secretary of defense, Shanahan spoke of renewed “great-power competition” with China and Russia, the central theme of the new, Mattis-crafted National Defense Strategy. In Senate testimony during his confirmation hearing in the summer of 2017, the longtime executive at the aerospace company Boeing supported sending additional coalition troops to Afghanistan, “buttressing” NATO in part by deploying American military personnel to the Baltics and Poland to counter Russia, and reassuring U.S. allies in Asia of Washington’s commitment to maintaining the “security architecture of the Pacific Rim.”

Shanahan, in fact, made the very argument that many critics of Trump’s Syria pullout are expressing at the moment: that the lasting defeat of ISIS and its imitators depends not just on wiping out the terrorist organization on the ground, but also on working with partners to achieve a “political” resolution to the conflict that curbs Iranian and Russian influence in the country and produces a “legitimate” Syrian government. Reflecting on the “disastrous” lessons from the Obama administration’s military withdrawal from Iraq and Libya, he noted that the United States “must stay engaged in the fight and not walk away, because, as hard as it is, the alternative is worse.”

“Much of Pat’s view of the world has been formed by his relationship with Jim Mattis,” says Jim Albaugh, a retired Boeing executive who was Shanahan’s boss in the company’s defense division and, later, on the commercial side. Albaugh has stayed close with Shanahan and also knows Mattis personally.

Yet what’s most striking is that even those close to Shanahan weren’t sure how to answer when I asked what his firm foreign-policy views are, beyond pointing to his efforts to ensure that the U.S. military has a competitive edge and is ready for combat. “He’s pretty apolitical,” Albaugh told me, an assessment echoed by others I interviewed who know Shanahan. (While at Boeing, Shanahan donated to both Democratic and Republican political candidates.)

“As secretary of defense, even as acting, he’s going to have to show those cards,” says Rick Larsen, a Democratic representative from Washington State whose district includes a major Boeing production facility where Shanahan worked. “If it takes three months to get a new secretary in, even if it’s him, we don’t have three months to put a pause on the national-security strategy of the United States. We don’t have three months to wait to see how we’re gonna proceed on military-to-military relations with China.”

At the Pentagon—where he has focused on internal matters such as crafting annual budget requests and launching a process for migrating the department’s IT systems to the cloud, racking up only provisional achievements at best—Shanahan has described his role as the “chief operating officer.” He has, in other words, managed the internal execution of the vision articulated by Mattis, a legendary four-star general and “master strategist,” as Shanahan admiringly put it during his Senate confirmation hearing.

The 56-year-old Shanahan is an MIT-trained engineer and 31-year veteran of Boeing, most recently as a senior vice president for supply chain and operations, who acquired the nickname Mr. Fix-It for turning around beleaguered programs such as the development of the 787 Dreamliner passenger jet. Shanahan, who was reportedly not Mattis’s first choice for the deputy job, is a technocratic program manager through and through.

Read: James Mattis’s letter of resignation

Mattis seasons his remarks with quotes from statesmen and strategists such as Winston Churchill and George Shultz. Shanahan, by contrast, refers to a Pentagon office as the “obeya room” in homage to the Japanese corporate problem-solving technique, and cites Kodak as a cautionary tale for the consequences of failing to innovate. Whereas Mattis cast the National Defense Strategy as a means of bequeathing the free world as we know it to the next generation, Shanahan noted how “a risk-balanced, opportunity-driven approach will spark innovation and help protect our hard-earned culture of excellence from the unintended distortion of budgetary instability.”

While visiting U.S. soldiers in Iraq over Christmas, Trump praised Shanahan as a “good buyer” of military equipment, not some master strategist. “I’m in no rush” to replace him, the president declared. (Shanahan is only the third defense secretary to serve on an interim basis since the position was created in 1947.)

Shanahan has embraced some of the president’s pet projects. He’s championed increased sales of U.S.-made military goods and services to other countries, for example, and led Pentagon efforts to establish a new Space Force (an initiative Mattis at first resisted).

Riki Ellison, a friend of Shanahan’s and the chairman of the Missile Defense Advocacy Alliance, a nonpartisan organization that aims to build public support for missile-defense systems, told me that Shanahan’s competitive nature is useful at a time when the U.S. military is jockeying with China and Russia in domains ranging from space to the processes by which each power acquires its military capabilities. (Such acquisitions are what Shanahan “does best,” he said.)

But Shanahan can come across as less enthused about Trump’s ideas themselves than making the ideas work—of ingeniously solving the president’s problems, like a good engineer. “It’s pretty exciting,” he has said of the Space Force. “Over a very short period of time, it’s been thrust upon us to create and grow a new organization.”

“He’s not gonna dictate. He’s gonna follow what the president’s intent is,” Ellison said. Shanahan, who is succeeding a man Trump reportedly resented for slow-walking his directives, is “an efficient doer of things,” he told me.

As the aviation journalist Jon Ostrower, who spent years covering Shanahan at Boeing, recently wrote, Mr. Fix-It enjoyed “exemplary” relationships with his superiors at the company because he made sure “the leadership delivered what it promised.” Some observers, including the late Senator John McCain, have voiced concern that, beyond the president hitting it off with a fellow businessman at the Defense Department, a suspiciously cozy relationship is developing between the Trump administration and Boeing, one of the nation’s leading defense contractors. Ethics rules require Shanahan to recuse himself from Boeing-related matters at the Pentagon.

With Mattis’s departure, the last full-throated advocate of the principles that have guided U.S. foreign policy for decades has now left Trump’s inner circle, following in the footsteps of figures such as H. R. McMaster and Nikki Haley. Taking their place are disruptors (such as the president’s sovereigntist national-security adviser John Bolton) and doers (be it pragmatic implementers of Trumpism like Secretary of State Mike Pompeo or loyal foot soldiers like the UN ambassador nominee Heather Nauert).

Shanahan’s approach seems closest to that of Pompeo, who served in Congress but previously made a career in business as well. As something of an unknown quantity, Shanahan now appears to be auditioning before Trump, during a period when many of the president’s top aides—from his new chief of staff to his attorney general—are similarly in limbo as “acting” advisers.

Ellison didn’t pick a side when asked whether Shanahan’s view of the world is ultimately closer to Mattis’s or Trump’s. He acknowledged, however, that Shanahan doesn’t have Mattis’s foreign-policy pedigree or relationships around the world, and that “the Pentagon is so much more challenging than anything he’s ever done in his life” in terms of its massive budget and bureaucracy.

Read: The Woodward book comes for James Mattis

Hence why Trump’s decision to speed up Mattis’s exit and install Shanahan by the first of January 2019 has alarmed Adam Smith, a Washington State Democrat and the incoming chair of the House Armed Services Committee. Shanahan “does not have the comprehensive understanding of global national security threats that Secretary Mattis does,” Smith said in a statement. “Throwing him into the role of acting secretary with no notice in this way unnecessarily places the United States in a riskier position.”

Shanahan has certainly “earned the Mr. Fix-It” nickname, says Larsen, who from his perch on the House Armed Services Committee has also interacted with Shanahan since his arrival at the Defense Department. But now “the questions I’m going to have won’t be along the lines of, ‘How is the cloud-computing contracting problem going?’” he told me. “It will be focused on, ‘What’s your opinion of the Syria withdrawal? What’s your opinion of NATO? Will you be able to say no to the president or at least push back on the president and offer him advice that might be different than what he wants to do?’”

Over the past year and a half, Larsen reflected, Shanahan has struck him as “the Sergeant Friday of the Pentagon,” a reference to the fictional Dragnet detective who famously followed the facts wherever they led. The problem, Larsen told me, is that “the president maybe doesn’t like the facts.”