Editor's note: David Gergen is a senior political analyst for CNN and has been an adviser to four presidents. A graduate of Harvard Law School, he is a professor of public service and director of the Center for Public Leadership at Harvard University's Kennedy School of Government. Follow him on Twitter.
(CNN) -- The final presidential debate will range over world hotspots -- from Iran and Syria to Afghanistan and Iraq -- but if you listen closely, you will also hear an entirely different conversation: signals to voters back home trying to shape their choice in a slam-bang election.
A month ago, this final debate about foreign policy seemed faintly irrelevant.
In a series of polls asking voters to rank their most important issue, foreign policy consistently fell near the bottom. Only 6% chose "foreign policy and the Middle East" in an NBC News/Wall Street Journal poll. CBS News/New York Times posed an open-ended version of the same question -- foreign affairs did not even make the list of the top 10.
But the debates have transformed the election landscape. With the race in a dead heat 15 days from the election and this debate their final moment together, both candidates are scrambling to make their closing arguments to voters they still need. And even though Monday night is ostensibly about America's role in a jumbled world, they will surely seize upon it to serve domestic ends.
For President Obama, this is a major opportunity to hone in on the group that may be most important to his election: women. As pointed out by Ron Brownstein, one of the nation's best students of the interplay of politics and demography, Obama can win the election if he wins over more college-educated women in the Southeast and more non-college educated women in the upper Midwest. He has already made strong inroads with both, but needs a little more heft.
Obama's best way to do that is to convince women that he will not only protect our security but he will keep us out of war. He has argued in the past that he is doing just that by getting bin Laden and by extracting the U.S. from Iraq and Afghanistan.
He can advance his case by arguing that tough sanctions have led the United States and its allies to edge much closer to talks with Iran, which could defuse the possibility of an armed conflict. Presumably, the story leaked by the administration to The New York Times over the weekend about new talks with Iran was intended to set up exactly that conversation.
The Obama people also realize that they are presenting Romney with a tricky choice: either he can agree with Obama that more talks with Iran would be wise before any bombs fall, or he can take a harder line on Iran. The first choice risks Romney saying "me-too," but the second might make him seem just too bellicose -- George W. Bush revisited. Either way, he has to avoid that trap. Similar tough questions surround other issues, especially the growing dispute over whether the U.S. should intervene in Syria, a civil war spilling over into Turkey and Lebanon.
For Romney, a key imperative Monday night is to find a way to drum in his central message: He will be better than Obama in creating jobs, taming the deficits, and growing the economy.
On the surface, a foreign policy debate doesn't lend itself to that message. But a clever candidate could find a way to argue that the biggest threat to America's national security is economic weakness and demoralization at home. Military leaders stretching back to Eisenhower have successfully argued that peace comes through strength -- both in arms and in the economy.
It has been clear for some time that Obama and Romney are running increasingly different campaigns. Obama is tailoring messages and actions to groups that make up his coalition: women, minorities and youth.
Romney, on the other hand, is trying to win through a single message aimed at all: I can turn this economy around.
Each will try to advance their messaging strategies during the debate.
Finally, this last debate also presents an opportunity to detail who would be a better commander-in-chief. Obama has held a strong upper hand on this question throughout most of the campaign but since the first debate -- as in other areas -- Romney is closing in.
U.S. elections are rarely won on a particular foreign policy issue, but voters do care whether they feel confident and secure about the person in the White House who gets the 3 a.m. phone call. Obama has come a long way in burnishing those credentials since his candidacy of four years ago. But recent turmoil in the Middle East, and White House handling of it, has caused some uneasiness.
Romney, meanwhile, has often been clumsy on foreign affairs -- remember his ill-fated trip to Europe this past summer. But he has seems to have steadied a bit since then.
So, even though foreign policy issues rank low among the priorities of most American voters, the debate has emerged as yet another critical moment on the long, nail-biting race to November.
The opinions expressed in this commentary are solely those of David Gergen.