Like many military officers, Secretary Mattis never seemed interested in the cabinet politics that come with the position. He avoided fights with fiscal hawks in the White House over defense spending, even as defense hawks in Congress begged him to make the case for additional dollars.

Secretary Mattis seemed to run the Pentagon like it was a combatant command. After hundreds of billions in defense cuts under the Obama administration, he rightly made a priority of improving readiness. But that came at the expense of long-term overhaul, despite bipartisan support for efforts like growing the Navy to 355 ships.

Additionally, Gen. Mattis brought a warfighting-first perspective to public relations. With no background in politics, he undervalued the importance of engaging the public on national-security issues and scaled back the department’s public release of information. This had the perverse effect of reducing the department’s ability to persuade Congress and the public in important bureaucratic fights.