Scene from the 1991 movie "Black Hawk Down" about U.S. intervention in Somalia's civil war.

Barack Obama and John McCain touched on a topic in last night’s presidential debate about which the Church is the leading expert: Just War doctrine.

The candidates were asked by moderator Tom Brokaw if “we can establish tonight the Obama doctrine and the McCain doctrine for the use of United States combat forces in situations where there’s a humanitarian crisis, but it does not affect our national security.”

Obama said, “Well, we may not always have national security issues at stake, but we have moral issues at stake.”

And when genocide occurs, he suggested, “We have to consider it as part of our interests, our national interests, in intervening where possible.”

McCain also favored intervention in the case of clear-cut genocide, as in World War II’s Jewish Holocaust and the ethnic slaughter of Tutsis in Rwanda in the 1990s.

But he placed more stress than Obama on a key factor to be considered before deciding to intervene in a foreign conflict: the ability to make a positive difference by risking the lives of American soldiers.

Said McCain, “So you have to temper your decisions with the ability to beneficially affect the situation and realize you’re sending America’s most precious asset, American blood, into harm’s way.”

The Catechism of the Catholic Church specifies the four elements required for the legitimate use of military force in section no. 2309: Certain knowledge of “lasting and grave harm” being inflicted by the aggressor; other means of stopping the violence must have been shown to be ineffective; there must be “a serious prospect of success”; and the use of force must not produce greater evil than the initial aggression.

But, the Catechism stresses, “The evaluation of these conditions for moral legitimacy belongs to the prudential judgment of those who have responsibility for the common good.”

— Tom McFeely