Acting Defense Secretary Patrick Shanahan. (Aaron P. Bernstein/Reuters)
Contributing columnist

If he is confirmed as the next defense secretary, Patrick Shanahan will probably face more challenges than any Pentagon chief before him. Most important, he will face the most complex and difficult global security environment in our nation’s history.

To be sure, World War II starred more implacable foes. The Cold War was a 40-year existential threat. But never before have so many global and regional powers, rogue nations and nonstate actors converged in such an interconnected world.

China is the most significant competitor Shanahan will face, as it continues to pursue its goal of becoming the dominant nation in Asia and a significant player across the globe. The People’s Liberation Army is on a path to become a rival power the likes of which the United States has not seen since the military heyday of the Soviet Union. Beijing knows that any contest in Asia will probably be a naval and air-combat struggle, and it has prepared accordingly by developing sophisticated counterspace, counterair and countermaritime capabilities. These investments in weapons programs, coupled with profound organizational reforms, will leave the Chinese capable of projecting military power well beyond their shores.

Shanahan will also need to confront an emboldened Russia bent on undermining the United States by any means possible. Russian defense spending has doubled in the past decade, and Moscow has developed and fielded weapons systems designed to thwart the United States in a military contest near Russia’s borders. Moscow’s reliance on cyberwarfare has been effective at sowing uncertainty and worse; its new doctrine of using tactical nuclear weapons without triggering a strategic nuclear exchange is a particularly dangerous development.

In Iran, Shanahan will have to contend with a nation that has vivid nostalgia for its imperial past and aspirations for regional hegemony that come with it. It sees the U.S.-led order in the Middle East, including the existence of Israel, as a roadblock to that hegemony. And, while its military capabilities pale compared to Russia’s and China’s, Iran is investing aggressively in its military. It boasts the largest ballistic missile force in the region, and it effectively uses proxies, including designated terrorist groups, to further its military reach in the region.

North Korea continues to pose a major threat. Kim Jong Un’s primary objective is the survival of his regime, and he has long seen strategic weapons as the key to both deterring the United States from moving against him and coercing it and its allies to provide the assistance he needs to survive. Despite, and in part because of, President Trump’s unusual diplomacy, North Korea’s strategic weapons capability remains, sanctions have been loosened, and Kim has the most international credibility that he, his father or grandfather ever had. Kim continues to expand the regime’s conventional military capabilities with more realistic training, artillery upgrades, and close-range ballistic missiles that improve Pyongyang’s ability to strike regional U.S. and allied targets with little warning. The threat from the North will be front and center for Shanahan.

Meanwhile, radical Islamist terrorist groups continue to pose a threat to Americans and U.S. interests. Notwithstanding recent gains against the Islamic State, there are more extremists today in more countries around the globe than before 9/11. Powered by state failure brought about by poor governance, regional conflict and environmental challenges such as severe drought, we will need to defend ourselves from these groups for generations. As much as Shanahan tries to focus elsewhere, terrorism will demand his attention.

Shanahan also faces the need to modernize the U.S. military. As a recent congressional commission on which I served pointed out, the United States would struggle to win and could even lose a war against Russia or China. Our ability to fight a conventional war against our main geopolitical rivals has atrophied because we have been engaged in counterterrorism for the past 18 years, because our adversaries have made significant investments to counter our capabilities and because politics in Washington has hit the defense budget hard.

And finally, Shanahan will need to do all of this while working for the most isolationist president in memory. Whether it is not recognizing the threats or making it difficult for the United States to work with our allies, Trump will put the new secretary in a challenging position. Given that the predecessor, Jim Mattis, lost this battle, the odds of Shanahan managing this are not high, making his task of protecting the country today and preparing the department to protect it tomorrow a wickedly hard job.

Read more:

David Ignatius: There’s too much at stake for Trump to leave the Pentagon in limbo

David Ignatius: Patrick Shanahan could be what the Pentagon needs — if he doesn’t become Trump’s yes man

Josh Rogin: Inside Patrick Shanahan’s clash with Congress in Munich over Syria