I know that "campaign manager" is an obvious place to make changes if your campaign's not performing as well as you'd like. But "chief strategist" seems just as obvious to me--perhaps more so, particularly if you think Hillary has made some big strategic mistakes (anyone remember the inevitability candidate?) and continues to face some strategic challenges. And yet, after some initial chatter just before New Hampshire, we've heard very little about Mark Penn, but tons about Patti Solis Doyle, culminating with her ouster today.
The only explanation I can think of is that Penn is very close to both the Hillary and Bill wings of the Clinton campaign, while Doyle was only really close to Hillary, leaving the so-called "white boys" (Hillaryland's term for the people around Bill, not mine) free to plot against her.