After the White House announced that Susan Rice would be replacing Tom Donilon as the president's national security advisor, I asked a foreign policy analyst who is close to the White House if he thought the change in personnel portended a change in policy. "Sure," he said, sardonically. Susan will bring her magic wand and solve every problem in the world through intervention. He was mocking not Rice herself, but naïve activists who imagine that a more idealistic national security advisor will forge a more idealistic approach to the world. More than four years in, Barack Obama has figured out what kind of foreign-policy president he wants to be -- less the visionary of the 2008 campaign than the faithful steward of national interests who closes out the ruinous misadventures of the post-9/11 era and husbands, rather than recklessly spends, America's limited resources. And it is reasonable to assume that this strategic recoupment will necessarily define Rice's tenure, whatever her personal convictions. But I wonder if that's so. At first, after all, Secretary of State John Kerry looked a lot like his predecessor. Someone -- me, actually -- called him "Hillary Clinton in pants." But that hasn't been true at all. Hillary was an icon, with an iconic sense of her own role as America's face to the world; Kerry is a private figure enamored of back channels and shuttle diplomacy. Hillary was preoccupied with "cross-cutting" issues like the status of women; Kerry is a throwback who yearns to broker deals among sovereign states. And so he has frontally attacked deadlocked situations in Syria, Pakistan, and Palestine which his predecessor largely left to others. Good for him, I say. Rice and Donilon are more obviously dissimilar. Donilon is a political insider with a deep regard for process, a man committed more to the neutral principle of ensuring that all voices are heard than to any specific policy outcome. He is a cautious man who wins the plaudits of foreign-policy realists for helping Obama steer clear of reckless entanglements, in Syria and elsewhere. Rice is a foreign-policy professional with deep convictions and a blithe self-assurance about her own judgments. She is a morally driven figure who makes those same realists uncomfortable. Michele Flournoy, the former under secretary of defense, says that Rice "may be more willing to take action in support of our values than many others would be who are more realpolitik." The distinction is meaningful, but easily overdrawn. I once asked Rice if she considered herself idealistic, and she bridled. "`Idealistic' to me connotes believing in things or wanting things that are not achievable," she said. She would accept "principled," but she was fine with "pragmatic." At the United Nations, where she has been the U.S. ambassador, she is known for aggressively pushing American interests, not global goods. Rice also has an extremely well-developed instinct for where the president wants to be on any given issue, and will not stray beyond his views. She will wave no magic wands of intervention. Yes, she pushed the president to intervene in Libya; but she has not done so with Syria. She did not, intriguingly, join Hillary and former CIA director David Petraeus and others in urging the president last year to arm the rebels. So why does it matter that Susan Rice will be the next national security advisor rather than, say, the estimable Tony Blinken, the current deputy? Is it just a question of style -- of Rice's famously short fuse, her battle-tested skills as a turf warrior, her special relationship with the president as a fellow African-American superstar? All those things matter, and have already been subjected to a great deal of scrutiny (as in here, for example). But one senior administration official I spoke with said that the salient differences between Rice and Donilon are not in temperament but in outlook. Again, think of the analogy with Kerry, whose travel schedule and pubic oratory give the impression that he is tugging the White House deeper into the Middle East at the very moment it is trying to leave the region's savage conflicts behind. Kerry isn't doing this because he's a lone wolf, but because he knows the region so well and is passionately committed to sorting out its problems. Susan Rice has a different, if overlapping, set of commitments. She spent much of the eight years between Democratic administrations at the Brookings Institution writing about the connection between weak and failing states and American national security -- and, yes, humanitarian intervention. The one issue she made her own as ambassador to the U.N. was nation-building and peacekeeping in Africa. Both Rice and Kerry, in short, care deeply about the kind of intractable and generally unrewarding -- and morally urgent -- problems which have absorbed the energies of American statesmen since the end of the Cold War. The "pivot" to Asia, for which Donilon is given a good deal of credit, represents a recognition that the United States needs to prepare itself for both new opportunities and new threats in the region; but also a national exhaustion, even disgust, with the thankless task of peace-making, state-building, democracy promotion, and above all military intervention of the last generation. Americans don't want to meddle with the insides of countries any more. But the Middle East is going to keep tugging at the American sleeve. What is Washington going to do if not just Syria, but also Lebanon and Iraq, slide deeper into sectarian warfare? What if declining oil prices destabilize Saudi Arabia, or a third intifada breaks out in Palestine? The African success story is real; but so, at the same time, is state failure in much of the continent. In Dispensable Nation, Vali Nasr harshly criticizes Obama for favoring drones and counterinsurgency over diplomacy and development, and mocks the pivot to Asia as a kind of escapist fantasy. It's a one-sided narrative, but there's a lot of merit in it. So I wonder if Rice will rebalance the rebalancing, and remind Obama that America can not walk away from the world's weak and failing places. Egypt and Libya need the United States, no matter how vexing they are; and Washington needs to let Egypt's president, Mohammed Morsi, know that cracking down on Hamas will not be enough to buy American goodwill if he continues cracking down on his domestic opposition as well. Meanwhile, the rebels in Syria need the United States as well. Kerry has done Obama a favor by arranging with Moscow to bring the two sides together in Geneva, and thus buy more time for U.S. inaction. But the conference is almost mathematically certain to fail -- if it is held at all -- and then Washington will have to choose between obviously futile diplomatic encouragement and some form of military assistance, whether facilitated or provided directly. Is it such a foregone conclusion that Obama will continue to stand by as the body count mounts towards 100,000? The wisdom of restraint may come to feel intolerably craven. And Rice -- and Kerry -- may wind up urging him to arm the rebels. They might even work together! The Barack Obama we have come to know over the last four years is a deeply cautious man with an acute awareness of how noble-sounding missions can miscarry disastrously. And the economic failure he inherited has compelled him to argue for "nation-building at home" rather than abroad. But he is a complex man with an ambitious sense of his nation's destiny, and his own. Tom Donilon reinforced one side of Obama. Perhaps Susan Rice will reinforce the other.