Pornchai Kittiwongsakul / AFP / Getty Images U.S. Marines participate in a drill in Sattahip, Thailand, on Feb. 10, 2012, during Cobra Gold, a military exercise involving personnel from seven nations

Though the Republican presidential hopefuls are still duking it out among themselves, it seems the GOP has already thrown down the gauntlet on foreign policy. First and foremost, Republicans will show off their hawkish credentials and lambaste the Obama Administration over its supposed “appeasement” of the radical regime in Iran. More awkward, they’ll have to challenge Obama on the great dragon in the room — China.

That contest has already begun. In an op-ed in the Wall Street Journal last week, Mitt Romney trumpeted his anti–White House, anti-China talking points, painting Obama as an agent of American decline and “a near supplicant to Beijing.” Some commentators have already spelled out the misrepresentations in this depiction of Obama’s China policy, which has seen a reassertion of U.S. interests in the Asia-Pacific in recent months. They also point to the many similarities between Romney’s muscular posturing and what the Obama Administration has already set about doing to face the rising Asian hegemon.

(PHOTOS: Obama’s Asia Trip)

“The sum total of my approach,” Romney concludes, “will ensure that [the 21st century] is an American, not a Chinese century.” Yet that anxiety to prevent the dimming of American supremacy is one very much shared by the current President. Obama is a noted admirer of the recent work of Robert Kagan — a conservative pundit on Romney’s foreign policy team — whose new book, The World America Made, champions the importance of American power for the preservation of the international order.

Of course, by many indications, the U.S. remains the unmatched economic and military leviathan bestriding the planet. But, after the hurly-burly of this election year, Americans of all political stripes will have to face up to a reality obvious to most others elsewhere in the world: that the Pax Americana that briefly existed after the fall of the Soviet Union, that of a confident, dominant unipolar power, won’t have very long legs in the 21st century. Within the next few decades, China is projected to eclipse the U.S. as the world’s biggest economy. Where the U.S. Navy once marshaled the planet’s oceans unchallenged, it’s now finding itself increasingly checked by the aspirations and enhanced capabilities of other budding powers — China, of course, but even nations closer to Washington’s orbit, like India.

(MORE: Did America Bond with China’s Heir Apparent, Vice President Xi Jinping?)

The Obama Administration has done little to disguise its desire to shift the emphasis of the U.S.’s global grand strategy away from the Middle East and West Asia to the Pacific. This much discussed American “pivot” has led to agreements to deploy troops in Australia and a deeper American engagement in the region, including Washington steadily confronting China regarding its claims over the entirety of the South China Sea. In an interesting exchange with Kagan, Gideon Rachman — a columnist at the Financial Times and author of Zero-Sum Future, a dyspeptic look at the proverbial “post-American” 21st century — suggests the pivot is only prolonging an inevitable changing of the guard:

As for the U.S. pivot to Asia, I think it’s a predictable and rational response to rising Chinese power. But I’m not sure it will work. America’s allies in the region face an interesting dilemma. Japan, India, Australia, and South Korea have their most important trading relationship with China — and their most important strategic relationship with the United States. Unless China grossly overplays its hand and terrifies its neighbors, over time those economic ties will weigh more heavily than the military relationship with the United States. As a result, China’s influence in Asia will steadily increase — at the expense of the United States.

Of course, given the inscrutability of China’s military and political system, one can’t rule out Beijing “grossly overplaying its hand” in the future. Moreover, the emergence of an illiberal, nondemocratic global power raises real questions for international politics that can’t be glossed over by paeans to the strength of shared Sino-U.S. interests. For the U.S. to stay relevant in Asia, it has to play a delicate, subtle diplomatic game that ruffles few feathers, but still advances something of an American agenda. Zbigniew Brzezinski, Carter Administration foreign policy mandarin, offers this pragmatic vision for a U.S. Asia strategy:

Ultimately, the United States’ geopolitical role in the new East will have to be based on mediation, conciliation and balancing and not on military engagement in mainland Asia. An America cooperatively engaged in multilateral structures, cautiously supportive of India’s development, solidly tied to Japan and South Korea, and patiently expanding both bilateral as well as global cooperation with China is the best source of the balancing leverage needed for sustaining stability in the globally rising new East.

Last year, Obama was the first American President ever to attend the East Asia Forum, a “multilateral” institution that brings together Southeast Asia with China and India. While Romney and his Republican contemporaries red-scare in an election year, it’s this sort of granular (and boring) summitry — not an imperious, chest-thumping, overinflated sense of American purpose — that will shape the contours of regional geopolitics for decades to come. Whether American policymakers (and Presidents) can accept no longer being peerless top dogs is unclear. Others already have moved on, though. Hugh White, a leading Australian analyst, writes of the “Asian century” as a foregone conclusion:

In the Asian century, [Australia’s] Asian neighbours will for the first time be richer and stronger than its great and powerful friends. Australia will perhaps never again enjoy the familiar reassurance of being a very close ally of the world’s dominant power. But it can prosper in a stable, peaceful Asia if a new Pax Pacifica can be built that both accommodates Asia’s new power and keeps America engaged. How would that work? How can it be built? … These are the questions we really need to debate now.

These are questions that ought to be pondered in all political circles in the U.S. as well. Just don’t expect it to happen until after November this year.

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