Deval Patrick has more upside than Bloomberg, but he's far from a household name, wouldn't initially be able to participate in debates, and isn't obviously more compelling to D voters than a number of other well-qualified alternatives who are polling at 2-3%.
Plus, candidates who enter late have a terrible track record and D voters are quite happy with their choices. So for a new entrant, we're at a point of going VERY big (say, Oprah! big) or going home.
I do think next week's debate is a big opportunity for Booker, Harris and Klobuchar, who as I've said a number of times are more plausible nominees than a lot of the names being thrown out there.
