As President Barack Obama seeks to build his foreign policy legacy in this second term he must balance an unusual mix of circumstances.

On the one hand are the daunting challenges abroad, pitted against the spectacularly difficult political and economic ones at home.

But against this must also be balanced his good fortune at being in the Oval Office during a period of reasonably broad consensus among Americans about the kind of role the U.S. should take abroad.

That consensus embraces a certain amount of caution for the U.S. on the world stage, which seems a good fit for a generally cautious leader such as Obama.

Americans still want to see Washington's leadership respected abroad, but they seem much more hesitant to fall back on simply the shock-and-awe of its military might.

For example one Pew Research Poll in October found 63 per cent of Americans want the U.S. "less involved" in the Middle East, which has been the main focus of U.S. concerns for at least two generations now. Other soundings show they want out of Afghanistan even before the planned 2014 date for withdrawal.

We saw clear signs of this shift during the presidential debate on foreign policy when Republican Mitt Romney shucked off his former sabre-rattling pose to embrace this new consensus and agree with almost all Obama's positions.

Opportunism perhaps, but also recognition that America has changed.

Billions in cuts coming

In the broader historical sense, there seems today to be a national realization that the era of America being the world's policeman, which followed the ending of the Cold War two decades ago, is over.

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The coalition builder. Barack Obama with British PM David Cameron in front of No. 10 Downing St. in spring 2011. (Carolyn Kaster / Associated Press)

The sole-superpower role is neither advisable, nor affordable.

This new reality suggests Obama won't cave in to public demands to act forcefully abroad at the first sign of crisis (although this remains a question mark if Israel is involved).

As I wrote in a recent column, the Washington world of diplomatic and military think tanks is very much taken up these days with debates over whether America is in steep global decline, or is merely at a point where it demands more intelligent use of diminishing military and diplomatic capabilities.

For no U.S. administration can continue to sustain the current level of global primacy given the country's current debt situation, which is going to require hundreds of billions of dollars in cuts from military and foreign policy muscle.

What's more, a super-dominant U.S. is no longer welcomed by much of the world, and is actively resisted by such important new players as China, India, Brazil and Turkey.

Add to that the domestic discontent over foreign entanglements and Obama will need to be highly creative in his use of U.S. influence abroad.

Leading from behind

So what should we look for over this second term? First off, Obama is still a generally popular figure in much of the world and still heads the most influential nation on Earth.

Its economy is the richest, and its military, even after reductions, will be the most powerful well into the future.

His administration gains marks abroad partly in contrast to the grim Bush years, but also because its innate caution favours a greater reliance on real coalitions and alliances.

The essence of Obama's foreign policy has been summed up in the phrase "lead from behind."

The term emerged, in the Obama context, during the military campaign to oust Libyan tyrant Moammar Gadhafi, where the U.S. brought its high-tech military to the fight, but seemed content to allow Britain, France, and even Canada to take the lead in the early stages.

While his domestic critics howled that America appeared weak, he calmly manoeuvred other nations to shoulder more of the burden of leadership.

We should expect to see this same emphasis on coalitions on several pressing fronts now, including Iran.

Iran's alleged nuclear capabilities are probably America's most dangerous challenge, particularly as Israel draws closer to a possible attack and is pressing the U.S. to join in.

Instead, though, Obama has painstakingly built the broadest set of international sanctions in history to try and deter Iran from its weapons program.

And despite vowing to do "whatever it takes" (the diplomatic euphemism for a military strike) to prevent Iran getting nuclear weapons, the president will likely be very reluctant to approve high-risk action by the U.S. and Israel alone.

A similar approach can be seen in Afghanistan, where Obama has been vigorously arm-twisting NATO allies to pledge long-term economic aid and military training after the formal troop withdrawals at the end of 2014.

On Syria, Obama has made it clear the U.S. has no intention of leading a military intervention against the al-Assad regime, or of supplying current rebel groups with arms. Though it may well be doing some of this covertly, behind the scenes.

Demands on Washington to act will increase if massacres continue, but then so will Washington's insistence that the UN, NATO and some Arab nations also step up.

The pivot to China

In the Asia-Pacific region, Obama has ordered his famous "pivot" of U.S. naval forces to the Pacific to ensure China's rising power does not intimidate other nations and that crucial sea lanes remain open.

Here again, leadership will only operate through a broad coalition, as we are seeing through a growing alliance of sea powers, including Japan, South Korea, the Philippines, Thailand, and Vietnam, along with India, Australia and Canada.

There's a clear risk of escalating tensions in these waters, especially as China and its neighbours dispute sea boundaries and underwater resources.

Unlike the Cold War period, though, this still-forming coalition and China are not hardened foes, but active trading partners with a self-interest in each other's economic growth and stability.

Obama faces a host of serious problems over the next four years. Relations with Russia, Pakistan, Egypt and much of the Arab world need to be improved, and the global economy is fraught with dangers.

All these things will needs clear strategic focus as a well as strong nerve if the U.S. is to leverage its influence to good ends.

Coalitions alone can't solve all these problems, however. And the Obama legacy may well depend on whether creative statesmanship will be enhanced by his innate caution, or drowned by it.