Tonight's 90-minute vice presidential debate in Danville, Kentucky, will ostensibly give equal treatment to domestic and foreign policy issues, but a spate of recent international events (the Benghazi terrorist attack, "green-on-blue" killings in Afghanistan), and the predilections of moderator Martha Raddatz (the senior foreign affairs correspondent for ABC News) could bring global affairs to the forefront. Here are the X factors to look out for:

Martha Raddatz as Referee 

Tonight's format will include nine 10-minute segments in which "each candidate will have two minutes to respond to an opening question. The moderator will then lead a discussion." Will Raddatz aggressively rebut bogus assertions or sit by passively à la Jim Lehrer? Odds are, she won't want to be seen as a Lehrer-esque doormat, and on foreign policy issues, her depth of experience could be deadly for the candidates. "Raddatz has traveled to Pakistan and Afghanistan dozens of times, and to Iraq 21 times to cover the ongoing conflict," according to her bio. "She was on the last convoy out of Iraq and is the only television reporter allowed to cover a combat mission over Afghanistan in an F15 fighter jet, spending nearly 10 hours in the air on two separate missions."

Joe Biden's Experience

As the former chairman of the Senate Foreign Relations Committee with 36 years in Congress, Vice President Joe Biden has a great deal more foreign policy experience than Paul Ryan (even if all of that experience isn't necessarily flattering). By comparison, Ryan's 13 years in Congress have been consumed with domestic budgetary concerns in his role as chairman of the House Budget Committee. When Ryan does talk foreign policy, it's riddled with contradictions about everything from the Arab Spring to Chinese trade, as Slate's Fred Kaplan outlined in August. Biden will have an opportunity to speak from experience and a depth of knowledge, but don't look for him to go all wonky on free-trade agreements and international tariffs: The line everyone is anticipating is “Osama bin Laden is dead and General Motors is alive."

Benghazi Terror Attacks

What Ryan lacks for experience he can make up for in current events, which aren't playing out in the administration's favor. Yesterday, a House hearing revealed that State Department officials acknowledged they'd rejected repeated security requests in Benghazi during the weeks leading up to the September 11 attack. How come, and why is the FBI investigation into the killings taking so long?, Ryan might ask. Also, why did the administration repeatedly misstate the nature of the attacks? Expect hawkish rhetoric from Ryan on how Obama's "muddling" foreign policy has projected weakness in the Middle East. Expect Biden to push back that Republican budget cuts put embassy security in jeopardy around the world. 

Afghanistan

The uptick in so-called "green-on-blue" attacks by Afghan national security forces have deteriorated morale and jeopardized NATO's withdrawal strategy. That said, there aren't many differences between the two candidates on Afghanistan. Both Mitt Romney and Barack Obama support a withdrawal date of 2014. The major difference is that the Romney campaign opposes the fact that Obama announced that withdrawal date ahead of time, which allegedly gave the Taliban a signal they could wait this out. The Obama administration argues that setting a timeline was necessary to motivate Afghan national security forces.

Sequestration

A major policy position that effects both the U.S. economy and foreign policy is sequestration, or the $500 million in automatic cuts on defense and domestic spending that go into effect in January if Congress doesn't act. This is a foreign policy subject that's right in Ryan's wheelhouse: It involves budgets and numbers and not a lot of history. Still, Biden should be able to hold his own as well.