The protests and violence at American diplomatic missions across the Middle East and North Africa last week steered the 2012 presidential race into somewhat unchartered territory -- a debate over U.S. foreign policy.

While the topic certainly has not been absent in the rhetorical sparring between President Barack Obama and Republican nominee Mitt Romney, most of the campaign's focus thus far has been a battle over who has the best prescription to jolt a seemingly sluggish economic recovery.

But that changed last week. Romney's charge the United States was too quick to condemn a film that insulted Muslims before condemning the violence directed at American diplomatic missions abroad spurred Obama's claim that Romney had a tendency to "shoot first and aim later." And all this talk has opened a window on an area that is sure to consume a great deal of attention for whomever sits in the Oval Office next January.

The list of foreign policy challenges facing the United States is daunting -- including an awakening in the Arab world with a direction still unknown, a looming nuclear crisis with Iran and an uncertain future in Afghanistan (and neighboring Pakistan) once U.S. troops withdraw in 2014.

And let's not forget a bloody civil war in Syria, where the fate of thousands of biological and chemical weapons also hang in the balance. Then there are fiscal issues, from debt crises plaguing Europe to economic and geo-political challenges posed by a rising China.

Here is a look at some of the most pressing foreign policy issues facing the United States, and how the candidates who seek to lead the country approach them.

Iran

As the tension over Iran's disputed nuclear program ratchets up in the face of Israeli discord over the pace of current sanctions designed to curb Iran's nuclear ambitions, both Obama and Romney agree that Iran must not be allowed to develop a nuclear weapon.

"We are determined to prevent Iran from acquiring a nuclear weapon," Obama said in a press conference earlier this year alongside British Prime Minister David Cameron.

The Obama administration and European Union have launched parallel sanctions designed to squeeze Iran's petroleum sector and bring the economy to its knees as an incentive to get Iran to give up any military dimensions to its nuclear program.

In a recent interview with ABC News, Romney said he would draw the same line as Obama when it comes to Tehran's nuclear capacity.

"My red line is Iran may not have a nuclear weapon," he told ABC's George Stephanopoulos. "It is inappropriate for them to have the capacity to terrorize the world."

What ultimately constitutes that red line, though, is seemingly different for both men. For Obama, the Iranian government would have to take direct steps to actually acquire a weapon (which U.S. intelligence does not believe has happened yet), while Romney has said merely having a "nuclear capability" without actually moving ahead to produce a weapon would be a tipping point.

Syria

In Syria, where the carnage of the last year and a half has claimed tens of thousands of lives, the fate of the country's large stockpiles of chemical and biological weapons and whether to arm the opposition forces battling the regime of President Bashar al-Assad has drawn out differences between the two candidates.

What would trigger either overt or covert military involvement from the United States inside Syria?

"We have been very clear to the Assad regime, but also to the other players on the ground, that a red line for us is (when) we start seeing a whole bunch of chemical weapons moving around or being utilized," Obama said in a White House press conference last month. "That would change my calculus. That would change my equation."

As to supporting al-Assad's opposition, the administration has provide funds and non-lethal equipment like communications gear. In addition, the CIA is aiding in vetting rebel members for other countries who may be providing arms on their own.

For Romney, the Obama administration's policy of not providing arms to the Syrian opposition -- whose character and composition is still uncertain, according to administration officials -- is a mistake. The former Massachusetts governor supports greater American involvement in Syria.

"Instead of watching what's happening in Syria from a dispassionate distance, I would be leading in Syria by encouraging our friends there like the Turks and the Saudis to provide weapons to the insurgents in Syria," he said at the Faith and Freedom Coalition's annual briefing this summer.

Middle East peace process

No single foreign policy issue has bedeviled more U.S. presidents than the search for peace between Israelis and Palestinians.

Unlike previous presidents, for whom Mideast peace was mainly a focus in their second term, Obama entered office determined to work with all parties involved in the process to find a workable plan. But the effort did not go far, as the Israeli government continued to construct settlements in Palestinian areas and a unilateral quest for statehood by the Palestinians at the United Nations brought talks to a halt.

The relationship between Obama and Israeli Prime Minister Benjamin Netanyahu is cool, and while they have put on a public face of U.S./Israeli solidarity when they meet, it is understood the two don't have much of a personal rapport. Romney and Netanyahu, on the other hand, have a relationship that goes back decades from the time they were colleagues at the Boston Consulting Group.

While the style and rhetoric of Obama and Romney's approach to the Middle East may differ, there are rather modest differences in the substance of their positions on the conflict's root issues. Both men say their personal view is that Jersualem is the capital of Israel, but that issue must be negotiated between the Israelis and Palestinians -- a policy shared by previous presidential administrations, from both parties.