Reply #60: I agree, and there's another factor you don't mention.

[Jim Lane]

With a credible challenge from the left, Obama would spend the primary season defending himself against the attack that he's too conservative. Then, in November, all the money he spent on such advertising would redound to his benefit, as it would undermine Republican charges that he's too liberal. He would look like the sensible mainstream choice between the extreme left and the extreme right.

As against that, a serious primary challenge would leave behind some bitterness on the part of the supporters of the unsuccessful challenger.

I haven't really thought much about whether it would, on balance, be a good thing or a bad thing, because I see no chance that it will happen. None of the people who could do it will do it. A challenge by a total unknown will be ignored by the corporate media and won't do any significant good or harm.