Think of Susan Rice as the president’s assertive kid sister. Where he’s cool and deferential, she’s boisterous and sometimes abrasive. Where he avoids public confrontation, she often relishes it. They have different styles, but make no mistake: What Rice says out loud is often what Obama is thinking privately.

In appointing Rice to become national security adviser in place of Tom Donilon, Obama is trading a reliable gray sedan for a flashier but more temperamental sports car. He’s exchanging a private political dealmaker for a public provocateur. He’s replacing a man who dislikes taking risks, and has generally been good at avoiding them, with one of the more adventurous people in government.

And then there’s Benghazi: Obama is swapping a man who generally avoided the Sunday talk shows for someone who nearly committed career suicide for delivering the famous talking points (for which she was otherwise blameless). Enough, already, about Benghazi.

For an Obama administration that is struggling to find its voice in the second term, Rice’s elevation should be helpful. She will give the White House a compelling new focal point on foreign policy. People may not always agree with her, but they’ll know what she thinks. And perhaps she will galvanize sharper policy thinking from Obama himself, especially on Syria.

But the Rice nomination brings some obvious risks: She is not a quiet inside player in the tradition of Brent Scowcroft, who was Donilon’s role model as national security adviser. She’s more in the tradition of extroverted policy intellectuals such as Zbigniew Brzezinski and Henry Kissinger, who used the media and other channels to shape events.

It will be interesting to see how Rice shares the foreign-policy platform with Secretary of State John Kerry. White House officials say that Kerry will own the diplomatic space and that there shouldn’t be much overlap. But this pairing of ambitious policymakers conjures memories of past feuds between Kissinger and Secretary of State William Rogers, or Brze­zin­ski and Secretary of State Cyrus Vance.

Obama’s personal relationship with Rice will allow her to speak with special authority when she’s dealing with foreign leaders. But it could undercut Kerry, who is otherwise off to a strong start. The White House doesn’t envision Rice as a secret emissary, a la Kissinger. But foreign leaders may try to use her as a back channel anyway.

Rice will have trouble matching Donilon’s success as a process manager. Critics argue that he has been overly organized and top-down, but he has run a smooth interagency process: Paperwork is delivered on time to the Oval Office; decisions are made and implemented (or fuzzed because the president wants it that way). Donilon has been a firm and sometimes controlling presence, and he’s known as a hard taskmaster. But he gets the job done, in a way that Cabinet officials generally feel is fair. This won’t be easy for Rice to replicate.

“Tom is not given enough credit for running the process. He did that masterfully,” says Michele Flournoy, a former undersecretary of defense who sometimes butted heads with Donilon.

Rice’s biggest challenge is to help Obama project a more strategic view of foreign policy. Donilon took on the big issue of rebalancing U.S. diplomatic and military power toward Asia — culminating in this weekend’s summit between Obama and Chinese President Xi Jinping. But beyond the pivot to Asia, policymaking during the Donilon years sometimes seemed reactive and event-driven — closer to crisis management than systematic strategy. Obama said Wednesday that Donilon combined the strategic and tactical, but the world saw more of the latter.

Obama has some visionary ideas about the United States’ role in a changing world. They’re articulated in his speeches, penned by deputy national security adviser Ben Rhodes, but there’s often a lack of follow-through. That’s the first thing journalists often hear from foreign leaders: Where is your president on big issues? Why don’t we hear more from him? Perhaps Rice can help the White House send clearer policy messages to a world that is drifting without active and engaged U.S. leadership.

Rice has star power. She is smart, funny, profane and passionate. She can also be her own worst enemy — using sharp words or elbows when a softer touch would work better. In that sense, she and Obama are well-matched: The cool and cautious chief executive may benefit from a more hot-tempered national security adviser, and vice versa.