When President Obama and Mitt Romney sit down Monday night for the last of their three debates, two things should be immediately evident: there should be no pacing the stage or candidates’ getting into each other’s space, and there should be no veering into arguments over taxes.

This debate is about how America deals with the world — and how it should.

If the moderator, Bob Schieffer of CBS News, has his way, it will be the most substantive of the debates. He has outlined several topics: America’s role in the world, the continuing war in Afghanistan, managing the nuclear crisis with Iran and the resultant tensions with Israel, and how to deal with rise of China.

The most time, Mr. Schieffer has said, will be spent on the Arab uprisings, their aftermath and how the terrorist threat has changed since the attacks on Sept. 11, 2001. No doubt the two candidates will spar again, as they did in the second debate, about whether the Obama administration was ready for the attack in Benghazi, Libya, that killed J. Christopher Stevens, the American ambassador, and three other Americans. Mr. Romney was widely judged to not have had his most effective critique ready, and this time, presumably, he will be out to correct that.

The early line is that this is an opportunity for Mr. Obama to shine, and to repair the damage from the first debate. (He was already telling jokes the other night, at a dinner in New York, about his frequent mention of Osama bin Laden’s demise.)

But we can hope that it is a chance for both candidates to describe, at a level of detail they have not yet done, how they perceive the future of American power in the world. They view American power differently, a subject I try to grapple with at length in a piece in this Sunday’s Review, “The Debatable World.”

LIBYA AND BENGHAZI Both candidates will come ready for a fight on this topic, but the question is whether it is the right fight. Mr. Obama already admitted mistakes on “The Daily Show With Jon Stewart” and promised to get to the bottom of them, but the White House has been less than transparent about what kind of warnings filtered up from the intelligence agencies before the attack on the consulate, and whether there was a way that American security forces could have arrived sooner, perhaps in time to save some of the American lives. No doubt the argument will focus on a narrower issue: why the administration stuck so long to its story that this was a protest against a film that turned into something worse, rather than a preplanned attack by insurgents. For Mr. Romney, the task is to show that the Benghazi attack was symptomatic of bigger failings in the Middle East, a road he started down in the last debate, but an argument he never completed.