This is quoted from a blog which, in turn, was quoted by an NYT columnist. I'm going to check out that blogger though. Perhaps Mr. Jonathan Bernstein has more tidbits to share outside of the article quoted here:
"There is something different about contemporary parties than older parties, which is that national element. If I had to generalize -- and as with all generalizations, there are numerous exceptions -- what I'd say is this. In the nineteenth century and into the twentieth, local parties were able to control their nominations. Over the course of the twentieth century, and probably bottoming out sometime in the 1960s or 1970s, those parties lost control of nominations to candidates, who formed their own personal organizations...at the extremes, parties were relatively empty labels that independent candidates battled over. Over the last thirty or forty years, however, parties have evolved, developing strong national components that never existed in previous strong-party eras, and once again parties generally control their nominations. I certainly don't see anything in any of the cases this year (not just Sestak and Paul, but also Rubio, and the NY-23 special, and others) that seem to be about parties losing control over their own nominations, as opposed to party groups battling over those nominations.
Of course, no matter how strong parties get, as long as they are permeable and not strictly hierarchical they will still feature internal clashes, which will often play out in nomination fights. To the extent that independent candidates are also strong, they will sometimes clash with party choices. Really, I think that's the best way of looking at Arlen Specter. He obviously wasn't a creature of the Democratic Party establishment; he was, in many ways, a great example of the strong, independent candidates of an earlier era in American politics. The political system can still produce such creatures, but we're in a more partisan era now, and if it symbolizes anything, the demise of Arlen Specter is probably best seen as a sign of the strength of the new parties."