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.