Perhaps the decisive moment in the Massachusetts special election happened at the debate, when Scott Brown told Martha Coakley that he was running not for Ted Kennedy's seat but "the people's seat." The line cut through the idea that Democratic victory in the special election was inevitable simply because the Democrats were entitled to hold a seat they had occupied for decades.
A sense of entitlement is commonplace in political dynasties, whether you are talking about the Kennedys or the Bushes. Indeed, in retrospect we had a premonition of Brown's victory last year, when Caroline Kennedy's attempt to become the appointed senator from New York failed utterly. The public's anti-incumbent mood extends to those who believe they should rule because of their genetic heritage. This cuts across both parties.
Good candidates can make up for any disadvantages they might suffer thanks to their parentage. Even so: Beau Biden, Rory Reid, and Robin Carnahan--among many other Democrats and Republicans--ought to be a little worried after yesterday.