Be blasé about what you wish for
It would be some sort of good thing if some of the big blogs fomented a Primary Obama movement. Heck, maybe I'd sell a few more T-shirts.
Naturally, no one could have anticipated that Obama would be dreadful, and we must look forward and learn no lessons from the debacle, nor should we forgive the prematurely correct.
All that said, let's imagine that career progressives get behind the primary idea. It could happen, if only because movement-style activity is a good fundraising gimmick. Also, of course, because Obama is doing such yeoman work in devaluing his brand, try as his apologists do to keep buffing it. It may prove easier to energize progressives (with or without the scare quotes) by opposing Obama than by rallying behind him. Hard to say, as old love dies hard, but it's possible.
A Draft Dean movement, say, would IMHO be eminently gaggable. And much as I think Hillary Clinton is a better-than-average centrist, I cringe every time she's propped up as the One True Cure for what ails us. Wake me when she quits Obama's Cabinet with a blistering statement against his policies.
So, while I would like to see Obama face a vigorous primary challenge, the odds that the Democrats will be other than a roach motel for progressive energies are extraordinarily high.
I love a good show as much as anybody, so bring on the primary challenge. Just don't expect much from it, even if it comes.