Condi Rice's resume is long on activity, but short on accomplishment. It is hard to point to one thing and say "Wow, that was a great accomplishment!" She flew around the world, talked to foreign leaders and got some agreements signed. You could have replaced her with someone else and gotten pretty much the same results.
Romney needs to distance himself from both Bush and Obama. He can't go around saying "If you hate Obama, then vote for a Bush clone."