By mid-March, Senator Hillary Rodham Clinton’s campaign knew it had a problem with what it had once assumed was a reliable firewall — its support among superdelegates.
The fight for pledged delegates for the Democratic nomination was essentially over. Senator Barack Obama was ahead, after winning a series of caucuses in states that Mrs. Clinton virtually ignored.
Still, it became apparent that neither he nor Mrs. Clinton could claim the presidential nomination with pledged delegates alone, and the two would need superdelegates — elected officials and party activists — to fill the gap.
For Mrs. Clinton in particular, that signaled danger. The commanding lead she had held in superdelegates at the start of the contests — she was about 100 ahead of Mr. Obama — had dwindled by mid-March, to 12.
And superdelegates were showing an independence that the Clinton campaign had not counted on, not quite buying her argument that she was more electable than Mr. Obama.
The break in Mrs. Clinton’s supposed firewall turned out to be one of the most important factors in her campaign.
http://www.nytimes.com/2008/06/05/us/politics/05superdelegates.html?_r=1&oref=sloginFurther down, the article discusses Bill's impact on superdelegates. It sounds like he was a little too much for them.