And now, for some meaningless, but hopefully harmless, Sunday night commentary on the horserace...

Joe Klein's dispatch from the campaign trail on Sunday noted that both Hillary Clinton and Barack Obama had appropriated theme music from the now-defunct John Edwards campaign. Clinton has been playing John Mellencamp's "This Is Our Country," while Obama has been playing Bruce Springsteen's "The Rising." Obama's choice presumably has something to do with recent Springsteen's endorsement. But, as Klein observes, the song selection also signals something else:

What does this mean? Could it be...something significant? Actually, no: both are perfect for the populist pandering of the moment.
More about the campaign in a few days...but presidential politics sure can get tawdry in a hurry when the candidates are desperate.

Just to be clear, Klein isn't suggesting the candidates are desperate just because of their theme songs. He's basing that on his observations from the campaign trail. For more details, you can read his full dispatch here.

Assuming he's right--and Joe Klein usually is these days--it occurs to me you don't often see a situation like this, in which not one but both candidate are desperate.

But it also makes perfect sense.

Clinton is desperate because, without a signficant win in Pennsylvania, any tiny chance of taking the nomination would vanish altogether. But Obama is desperate, too, because if Clinton does win significantly, then she'll be able to continue her campaign, at least through the Indiana and North Carolina contests.

He'll remain the presumptive nominee, of course; the delegate math will look pretty much the same no matter what the result on Tuesday. But if Clinton stays in the race, it means more time spent fighting with Clinton rather than John McCain. It may also mean more persistent questioning about Obama's ability (or relative lack thereof) to win over working class whites.

--Jonathan Cohn