After the skaters and skiers, the curlers and hockey players head home at the end of the Olympic Winter Games, the one figure most worth watching for a hint of what awaits the Korean peninsula is the baggy-eyed ex-Marine known as “Mad Dog” or the “Warrior Monk.” 

Barring some catastrophe, the games will succeed in providing a respite from worries that North Korea and the United States are edging toward war — possibly with nuclear weapons. But a diversion is all it’s likely to be.

Chances are that North Korea’s decision to participate in the games represents little more than another of the tactical maneuvers it has perfected over decades. It’s possible that Kim Jong Un has blinked just a bit, but seems more likely that he is working just as hard on his nuclear warheads and ballistic missiles. 

Meanwhile, harsh language from President Trump and Vice President Mike Pence, plus the decision to drop a candidate for ambassador to South Korea who opposes a “bloody nose” strike at North Korea have led some to conclude Trump is considering just such an attack. In theory, it would serve as a warning short of launching a full-scale war. In practice, many experts doubt that once begun, a conflict could be contained.

Enter Secretary of Defense James Mattis, a retired Marine general.

Because Trump seems to have a thing for military men, because of Mattis’ fearsome reputation as a ground commander and because of his responsibility for America’s vast war-making capability, his voice is likely to be highly influential. So far, he hasn’t given a firm indication where he would come down on military action against North Korea.

Mattis is unafraid to unleash the U.S. military in what he considers the right circumstances. But he also is regarded as something of a scholar, and he has first-hand knowledge of how things can go badly wrong. He privately opposed the U.S. invasion of Iraq in 2003, ended up commanding 25,000 Marines charging toward Baghdad, and witnessed the messy aftermath.

CNN Pentagon correspondent Barbara Starr started her recent analysis this way: “Defense Secretary James Mattis begins his second year in the Trump Administration with perhaps just one absolutely crucial task — stopping President Donald Trump from going to war against North Korea.”

That may be overstating it a bit, but you get the idea how important this is.

While Kim’s motives remain opaque, there have been signals that Washington is reconsidering its options. This New York Times report describes a split among senior officials surrounding Trump — National Security Adviser H.R. McMaster on one side, and Mattis and Secretary of State Rex Tillerson on the other. Tillerson appears to have little influence, making Mattis all the more important.

McMaster, like the others, is said to still prefer a diplomatic solution, but wants the Pentagon to present Trump with more military options. The Times quotes officials as saying the Pentagon is worried Trump will move too quickly toward military action.

James Jeffrey, a former U.S. ambassador to Turkey and Iraq, says McMaster seems to be following a Cold War-era script that includes riskier military preparations to get the attention of North Korea and China. 

After months of vetting, the Trump administration also pulled the plug on the nomination of Victor Cha as ambassador to South Korea. Cha isn’t known as a softie when it comes to North Korea. But opposing a “bloody nose” strike was apparently enough to kill his nomination.

After it was pulled, Cha outlined his views in the Washington Post. If the U.S. considers Kim irrational, such an attack would put American citizens in South Korea — a population the size of Pittsburgh or Cincinnati — at risk “on the assumption that a crazy and undeterrable dictator will be rationally cowed by a demonstration of U.S. kinetic power.”

Instead, he argued for building on existing sanctions, supplying more sophisticated weapons to South Korea and Japan, imposing a blockade to prevent North Korea from nuclear proliferation and continuing to prepare for a defensive war.

So where might Mattis come down on all of this? He has stood out in the Trump administration by arguing against the use of torture and for the importance of alliances. He has been careful with public statements, and in the case of North Korea still emphasizes diplomacy — backed by military preparedness. If he starts moving off of that formulation, it could be very significant.

As bad as Iraq was, a war on the Korean peninsula probably would be much worse. The threat of chemical and biological weapons never materialized in Iraq. In North Korea they are a real possibility — along with nuclear weapons.

The New Yorker’s Dexter Filkins quotes Mattis as saying after a speech several years ago that he would have considered resigning his military command if he had been asked by a civilian leader to do something “unethical, immoral or … felony stupid.” But he also stressed the importance of chain of command. “Words like ‘You serve at the pleasure of the President’ — you can’t say, ‘Those words only count when I agree, and the President agrees with me,’” Mattis said. 

Mattis is in a tough spot that’s likely to get tougher. As the situation develops, it will be important to listen very carefully to what he has to say.