I have to say, I am thrilled that Pennsylvania is finally voting. It seems like an age since the last primary or caucus, and the press has already shown it has the attention span of a three-year old and that without the immediate specter of horse races to analyze or polls to parse, it will mindlessly pursue the first shiny object that catches its attention. So, if only for giving us a temporary respite from questions like "Is Rev. Jeremiah Wright as patriotic as Barack Obama?" (wtf?), thank you Pennsylvania.
That being said, this is a totally meaningless primary. There is no likely outcome which could seriously change the dynamics of the race.
Let's break it down. Barring something cataclysmic, Clinton cannot win the Democratic primary. She is expected to win Pennsylvania solidly, but the models all have incorporated that prediction and it isn't enough. A huge win -- say, 25 points -- might qualify as cataclysmic, but that's not going to happen. On the reverse side, while most people consider anything less than a 7-point win for Clinton to be a mortal wound to her campaign, she's not going to withdraw after winning Pennsylvania, so even a narrow victory won't push her out. Obama would have to score an exceedingly improbable upset (or maybe lose by just 1 or 2 points) for there to be any hope of Clinton exiting the race.
In absence of those two exceedingly unlikely scenario, the state of the Democratic race will be the exact same tomorrow as it was yesterday: Clinton remains in with only a negligible shot to win. Never has so much been said about a race with such little import.