Extended primaries almost always damage the eventual candidate. The "making her a better candidate" argument doesn't hold true now, though it had merit a few weeks ago.
In this instance I think Bernie staying in won't hurt Hillary.
Guys, we have to dispel this notion that Barack Obama doesn't know what he's doing.
He knows what he is doing.
He is undergoing a systematic transformation of this country... we don't want to be like the rest of the world! We are the United States of America, the single greatest nation in the history of the world!
