Secretary of Defense Jim Mattis has given everything to America: 44 years in the Marine Corps and 2 years of service at the Pentagon. But if he is open to a new challenge and responsibility, he should become the next NATO secretary general.

A longtime supporter of the alliance and of its need for European member states and Canada to spend more on defense and more of their defense budgets on equipment, Mattis would be a natural fit. Indeed, Mattis would be the most natural fit of anyone on Earth. First, he retains specific military experience with NATO from his time as the commanding general of NATO's Transformation Command. Second, Mattis is keenly astute to NATO's mission, capabilities, and vulnerabilities from his time as Defense secretary.

Over the past two years, Mattis has prioritized his relationship building with allies just as he simultaneously sought to push them to do more to fill in NATO's war-fighting weaknesses. President Trump deserves credit for his pressure campaign on the Europeans here, but without Mattis building NATO member confidence in America's ongoing commitment, he wouldn't have succeeded. The dividends of Mattis' leadership alongside current NATO secretary general, Jens Stoltenberg, are clear to see. NATO has improved its sea control and logistical trains and its ability to contest enemy air defense strongholds.

Yet Mattis' appointment to NATO command would be good for one final reason: in that as secretary general Mattis would be freed to support the alliance's mission without need to defer to other political leaders. Mattis would also be the first U.S. secretary general in history. In short, this is an appointment he is suited for and most certainly deserves.