Shift at Top May Mean Shift in Tone for Clinton - New York Times

I think that Penn's kind of sort of firing is unlikely to pull it out for Hillary Clinton at this late date, but Geoff Garin does seem to be a breath of fresh air.

That being said, Josh Marshall published a reader letter that nails the Penn problem on the head:

....increasingly I think Penn is the main reason. His faults suffused and defined her campaign - think small and narrow, don't change anything that worked for Bill, don't roll your proposals into a larger vision, don't suggest that you bring anything to the table but stolidity and experience - and, for targeted voters only, emphasize your gender. Penn took one of the most popular Democrats of the last 40 years and made her into a one-note bore.

Mark Penn and his "microtargeting".

Hillary is not Bill, and something sucked much the life out of her campaign.

It's why she seems better in the debates, there, it's just her and her knowledge.