The candidates hoping to succeed President Barack Obama are working to distinguish themselves from one another on a host of foreign-policy issues. To name just a few: how to counter the Islamic State terror group, how to respond to a newly assertive Russia, and how to shape relations with an increasingly confident and capable China. 

However divergent their views may be on those challenges, there is at least one judgement they would all likely support: trends in the Asia–Pacific region will increasingly shape world order and affect America's national interests. Kurt Campbell and Ely Ratner noted last year that the region houses "more than half of the world's population … the largest democracy in the world (India), the second- and third-largest economies (China and Japan), the most populous Muslim-majority nation (Indonesia), and seven of the ten largest armies." According to the Asian Development Bank (ADB), they continued, the region will account for about half of gross world product and be home to four of the world’s biggest economies before the middle of this century.

Given the region's current and projected weight, it is not surprising that, as Senator Marco Rubio (R–FL) observed, America's "rebalance to Asia is a bipartisan concept." Unfortunately, though, at least four phenomena challenge its viability as a pillar of US foreign policy.

First, an arc of disorder has enveloped much of the Levant. President Obama came into office with the conviction that the United States had a strategic opportunity-cum-imperative to prioritise the Asia–Pacific if and as it wound down its interventions in Afghanistan and Iraq. In late 2011, secretary of state Hillary Clinton penned a widely cited exposition of that proposition in Foreign Policy, and in January 2012, the administration formalised her recommendation with its Defense Strategic Guidance.  

At the time of that document's release, it was uncertain how the Middle East and North Africa would evolve in response to the revolutions that had begun in late 2010. Today, however, their preliminary results are clearer: IS has wreaked havoc in Syria and Iraq, plundering its way to the storied ruins of Palmyra. The United Nations Security Council released a report last month warning that "there are more than 25,000 foreign terrorist fighters involved [in the activities of various al Qaeda associates] from more than 100 member states." Libya and Yemen, meanwhile, continue to degenerate. The death sentences given to Mohamed Morsi and more than 100 others are likely to provoke further waves of sectarian recrimination in Egypt.  

In view of such developments, the United States finds itself compelled to reprioritise a region from which it thought it had achieved at least a short-term extrication. A White House veteran recently told the The Economist that "it never felt like we pivoted away from the Middle East. About 80 per cent of our main meetings at the National Security Council have focused on the Middle East."

The second challenge to the rebalance comes from a slow-moving conflict of attrition between Russian agents and Ukrainian resistance. While it is unclear whether Russian President Vladimir Putin's course will lead him to adventurism in other non-NATO members along Russia's immediate western periphery, the prospect has forced the United States to reevaluate the contours of its interactions with Russia and assess whether Europe's post-Cold War peace was an aberration in the continent's bloody history. 

The Defense Department is considering whether to station battle tanks, infantry-fighting vehicles, and comparable weaponry for a brigade of 3,000 to 5,000 US troops in Eastern Europe; the New York Times observed it "would represent the first time since the end of the Cold War that the United States has stationed heavy military equipment in the newer NATO member nations in Eastern Europe that had once been part of the Soviet sphere of influence." 

The third challenge arises from China's geoeconomic statecraft. Whether one considers its proposal for a Regional Comprehensive Economic Partnership or its "one belt, one road" initiative, China will play an increasingly large role in the economic vitality of its neighbors — not simply through exports, but also through infrastructure investment that they sorely need (a 2009 study by the ADB estimated that Asia would have to invest some $8 trillion in infrastructure between 2010 and 2020).

Most of China's neighbours would prefer a robust, sustained US presence in the Asia–Pacific. With the US Senate having voted for Trade Promotion Authority in order to complete the Trans-Pacific Partnership (TPP), strong US regional leadership seems assured. Considering that the 12 countries covered by the TPP account for some two-fifths of gross world product, such an outcome would be an important strategic victory for the United States. Still, on balance, it will become harder for them to resist the strategic preferences of a neighbour that possesses a rapidly growing economy and is a permanent geographic fixture. Per Marx's rendering of Hegel — "merely quantitative differences beyond a certain point pass into qualitative changes" — the accumulation of China's incremental reclamations and outpost fortifications within the South China Sea, occurring within the context of its commitment to a "nine-dash line" whose interpretation remains ambiguous, will inevitably change the region's order.

The fourth challenge to the rebalance is the weakening of a consensus that has guided US policy towards China for more than four decades, across eight administrations: namely, that the United States should engage China while hedging against a more assertive, even aggressive, turn in the mainland's conduct. This shift is partly due to the recognition that, contrary to widespread Western predictions, the growth of an enormous middle class in China and the leadership's adoption of incremental economic reforms have not produced widespread political liberalisation. It also owes to the calcification of strategic mistrust between the two countries — most apparent in their disagreements over China's course of land reclamation in the South China Sea, but also evident on a range of other issues. Regarding the familiar "engage but hedge" mantra, more US observers believe the fruits of US–China cooperation are small in view of America's 35-year-old project to integrate China into the world economic order. They also contend that hedging is antiquated. One hedges if one is unsure about another's intentions. They argue that, at least in the Asia–Pacific, China's objectives are clear: to weaken America's network of alliances and replace the United States as the region's preeminent power.

The United States lost critical time to shape the Asia–Pacific's order in the decade after 9/11, a reality it has aimed to redress in recent years. The gap in comprehensive national power between it and China as well as the underdevelopment of regional economic integration mean it can still play a significant role in the Asia–Pacific's trajectory. Still, China's influence in the region and the sophistication of what Evan Feigenbaum has called the "new pan-Asianism" will both increase substantially in the decade out to 2025 — with or without America's involvement. The late founding father of Singapore, Lee Kuan Yew, explained in late 2011 that "Americans seem to think that Asia is like a movie and that you can freeze developments out here whenever the US becomes intensely involved elsewhere in the world. If the United States wants to substantially affect the strategic evolution of Asia, it cannot come and go."

The United States should help contain the threats that the Middle East's convulsions pose to the region's order, but it should not get dragged into its maelstrom of upheavals. Its vital national interests are not at stake, and its experiences in Iraq and Afghanistan should caution it against believing that the use of heavy military force will substantially alter the region's course. Similarly, it has an interest in maintaining a stable balance of power in western Europe, but not in allowing the machinations of a stagnating Russian power to drag it into a war over Crimea or other territories that matter little for its own security. Neither the internecine struggles of the Levant nor Vladimir Putin's opportunism along his immediate western periphery changes the reality that the Asia–Pacific will play an ever-increasing role in shaping the world's economic, security, and strategic orders. The United States will find it more difficult to consolidate its Asian–Pacific perch with each successive round of preoccupation outside that theater, particularly if it proves unable to compete with China's regional economic diplomacy or its allies conclude that it seeks to contain the mainland

Between 9/11 and the Obama administration's announcement of the pivot, observers around the world questioned whether the United States would have the wisdom to shift the balance of its strategic equities to the Asia–Pacific, not whether it had the capacity to do so. If, however, having avowed the necessity of that recalibration, it does not follow through, competitors and allies alike will be more likely to conclude that it lacks precisely that capacity. That conclusion would undermine America's ability to compete in the crucible of world order.