Why is that?
Well, if you know your (American) history, you'll surely realise that the Kennedy name most certainly bears much more weight than just another Democrat controlled Senate seat. It takes much more to defeat a Kennedy than any other Democrat you care to think of. And not just that. Whichever Democrat successor comes along will have a much higher mountain to climb than any challenging Republican. It is not easy to fill a Kennedy shoe, let alone shoes.
So, while Obama must certainly take notice of what happened in Massachusetts, there's at the same time more and less to it than most analysts ("analysts"?) would have you believe. Just give it a minutes honest thought, and you'll see what I mean.
Go on! Do it. Now...