http://www.realclearpolitics.com/articles/2008/04/the_casey_fly_in_the_clinton_o.htmlEnter the Casey endorsement: the proverbial fly in Clinton's political ointment. Before Casey, the Clinton scenario was entering final rehearsals. She had corralled virtually every major politico in the state, was leading by double digits, and was apparently on her way to an impressive win. The Casey endorsement changes all that in both subtle and not so subtle ways.
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Casey's endorsement will also offer Obama some much needed momentum during the final three week push in Pennsylvania. Rather than stall the Clinton campaign, it's more likely to energize the Obama campaign, and what Obama critically needs in Pennsylvania during the final push is a lift. Casey, who will personally travel to many campaign stops with Obama and help him navigate through the often Byzantine world of state politics, will give him that momentum.
Finally the Casey endorsement may also help Obama corral more super delegates. Not widely reported has been the considerable deficit in Pennsylvania super delegates for Obama. Of the state's 29 supers, Casey becomes only the fourth to side with Obama. His endorsement now offers the yet undeclared super delegates cover and an excuse to endorse Obama.
The take away point here is that the Casey endorsement may be a game-ender, a final speed bump for Clinton that blocks any remaining viable path to the nomination. She needs to win Pennsylvania big, and Casey's presence in the race makes it hard for her to do that. Clinton probably still wins the state-but not by enough to allow her to continue the race past Pennsylvania.