Before I get to those reasons, let me bury the flap over Rice's minimal role in the Benghazi brouhaha. In appearances on several television talk shows after the attack, she said it was a spontaneous response to a notorious anti-Muslim YouTube video. Her remarks were based on talking points she'd been given in an intelligence briefing. She stressed that her information was incomplete pending further investigation.
You might fault Rice for not probing further, since news reports were already alluding to terrorist involvement. She might have done well to recall how Colin Powell was conned by his intel briefers about WMD in Iraq before his infamous 2003 speech at the United Nations. However, her repeat of her briefers' take on an assault still shrouded in CIA secrecy was hardly a sin.
A far more important issue is whether the U.N. ambassador has the proper temperament and background to succeed Hillary Clinton. It is here that the spotlight should be shone.
No doubt Rice is a highly intelligent woman, with degrees from Stanford and Oxford. But she has established a reputation for brusqueness and bluster that raises real questions about her suitability for the job.
She has riled European diplomats at the United Nations with her public criticism of their positions on Iran negotiations and other issues. She denounced Russian and Chinese vetoes of a Security Council resolution on Syria as "disgusting" and "shameful." That may well have been true, but such public displays of moral fervor will hardly help America's top foreign-policy emissary negotiate behind the scenes.
Equally worrying is the lack of heft and breadth in Rice's experience. During the Clinton administration, she worked on peacekeeping issues at the National Security Council and as assistant secretary of state for Africa. (She famously demanded that U.S. troops be sent to Sudan to prevent a genocide in the Darfur region - an idea that thankfully gained no traction.)
As U.N. ambassador, Rice helped persuade the president to endorse NATO intervention in Libya, but she has hewed to his reluctance to help the opposition in Syria, where the killing of civilians is far worse and the strategic stakes far greater. And the U.N. microcosm does not teach the skills she would need to manage America's relationships with the real world.
The next secretary of state will have to deal with a rising China and its nervous Asian neighbors. She or he will have to handle a convulsing Middle East and South Asia. Rice has expertise in none of these areas, and personal relationships with none of the region's leaders.
Kerry, on the other hand, with 27 years on the Foreign Relations Committee, knows every global player. Example: In 2009, when Afghan President Hamid Karzai flew into a dither and refused to sanction a presidential runoff election, Obama dispatched the Democratic senator from Massachusetts, who patiently walked Karzai around his Kabul residence for hours and won his acquiescence.
I can't imagine Rice doing something similar. Perhaps it's unfair, but I can only picture her demanding that Karzai get his act together, now.
Of course, the strongest card Rice has to play is that she and Obama are buddies. This friendship was forged when she abandoned the Clinton camp to join Obama's 2008 campaign.
However, looking back at another woman named Rice (Condoleezza), who parlayed a campaign friendship with George W. Bush into high office, I don't regard pal-ship with POTUS as a guarantee of good performance. It took the first Rice several years before she shook off her buddy role and finally found her own strong, independent foreign-policy voice.
Obama, who has kept foreign-policy decisions close during his first term, will need to delegate more as he focuses on fixing domestic problems. The foreign-policy challenges the country faces will be huge. He needs someone with the broad global experience of Clinton, not someone learning on the job.
The president shouldn't let the Republican critique of Rice box him in to the wrong choice. And Republicans would do better to button their lips.
Trudy Rubin can be reached at email@example.com.