Let me go on record as saying that it's wasted energy: Obama will win the nomination. He's ahead by every metric that counts. Clinton(s) only bests him in ability and willingness to scrape the bottom of the political tactics barrel. But come May 6, when Obama wins big in North Carolina and probably takes Indiana, all this will be forgotten.
Now, that doesn't mean I think Clinton(s) will withdraw or concede. It's still an open question whether they'll take their smarmy sense of entitlement to the convention in August. But at the end of the day, I predict Obama will prevail.
There is danger, of course, in how much damage is done to him come the general election, but the fundamentals are still in place for this to be a strong Demo year. (Hell, that's why Clinton(s) are fighting so hard. They know that whoever wins the nomination has a large chance of winning in Nov.) Bill and Hill could kill him in a death by a thousand cuts. They could implode the party with a floor fight. Their diehard supporters could sit out the election, depriving him of a fairly large share of Democratic votes. Any number of awful things could happen between now and November.
Is there cause for concern? Sure. But as of right now, it still looks good for Obama. It's myopic to lose sight of his strengths based on one primary.