Especially for Hillary, who is likely to seek someone younger who is ready for the presidency and won't draw too much attention to himself. I don't like comparisons, but O'Malley seems to be the Democratic equivalent to Tim Pawlenty.
I was literally about to suggest the same thing.
Yes, I agree. He's broadly acceptable to the major constituencies within the party and on paper he looks great. But if he was our nominee I would remind myself that he's good on the issues and then take some NoDoz to get through the campaign.