Via Atrios, here's yet more evidence that team Clinton had planned for Hillary to sew up the nomination early and really hadn't come up with a plan for what they would do if she didn't:
The Democratic primary in Pennsylvania, which will be held on April 22nd, requires voters to pick among pledged delegates, rather than candidates. Thus it's vitally important that candidates pick a slate of pledged delegate candidates well in advance of the primary.
As of now, Obama has a full slate of delegate candidates. Clinton is short by 10 percent, despite having the full backing (and presumably the advice) of Gov. Ed Rendell and Philly Mayor Nutter. What's more, Clinton would have twice as many unfilled candidacies if not for Gov. Rendell extending the deadline. Yes, people are even cheating for her, and she's still blowing it.
Again, Clinton's campaign had all the insider advantages a campaign could reasonably hope for: money, endorsements, experience, a good candidate, etc. By ignoring whatever isn't immediately in front of it and by not doing its homework, the campaign is making really stupid mistakes. Rookie mistakes. (The experienced candidate, my butt.) It was dealt a great hand, and it's not playing it very well.
*By "brittle," I refer to this 2002 article in the Atlantic Monthly about security systems. It cites a security expert who notes that every security system will eventually fail. The good ones manage to fail without compromising everything. Example: the metal detectors at Denver International Airport are at the main terminal, rather than at individual concourses. Suppose TSA discovers that one of those metal detectors has been unplugged for several hours. They'll have to evacuate the entire airport (rather than just one terminal) to remedy the situation. That's brittle.