An explanation from a reader:
Jonah, I suspect they’re doing this to make a controversy over her, which highlights for everyone that the Bushies have a prominent African-American woman on their team. Cynical, yes. Open to criticism, yes. But this is a matter of taste and manners. Clinton sent out Janet Reno on the stump, and few complained that it made her look partial. You can see why they might not send a Tony Lake or Sandy Berger.