John Dickerson of Slate also lays out the media’s case for Clinton needing a big win in Pennsylvania tonight.  How big of a margin will Clinton need in the Pennsylvania primary?

That number will be determined by a complicated and unknowable formula composed of press reaction, superdelegate calculations, and the constancy of Clinton’s own supporters. Clinton may win by the numbers but not by enough to keep superdelegates from continuing to move to Obama or to keep one of her key supporters from saying she should pack it in. She may win, but Obama may show that he’s made in-roads with blue-collar voters, the linchpin voting bloc with which he’s had trouble.

Continuing on our theme of extracting meaning from Pennsylvania primary results today, Adam Nagourney says that a win will need to be in the double digits for the Clinton campaign to really be able to claim victory.

[I]f Mrs. Clinton defeats Mr. Obama by a significant margin – think over 10 percent – it would give her the rationale to go on. Depending on what exit polls reveal about the nature of Mr. Obama’s loss – in particular, is he continuing to struggle among white blue-collar voters? — it would reinforce questions Mrs. Clinton’s aides have been pressing about Mr. Obama’s general election appeal, giving her one more argument to use with superdelegates.

He goes on to say that 6-9% will mean that she continues, but isn’t helped much by the victory.  Below 5% would mean increasing calls for her to leave the race, calls she may not be able to afford to ignore since her campaign is now broke.

This morning, several MSNBC analysts weighed in.  Tim Russert explains why this is an issue, which is to say why a win might not simply be a win:

Becuase she has to make the case, she has to provide the rationale, to superdelegates and donors that she has a reasonable chance of winning this nomination and its worth their effort to consider to give her an additional look.

So, how big of a win will she need?

Tim Russert:

She had been ahead by 20. She would like to win by double-digits, that would be convincing. … She’s in debt, she owes a lot of her vendors.

Andrea Mitchell:

[The Clinton campagin needs] to get close to double-digits … to bring out those undecided voters, to motivate people. Because, I got to tell you, they are broke, they are in debt.

Mike Barnicle:

To sustain herself, she’s going to have to win by at least 10 points.

In today’s Wall Street Journal, Amy Chozick puts to paper the thoughts of most of the media when she writes that Senator Clinton needs to win Pennsylvania big.

Anything less than a double-digit victory could solidify the perception that Illinois Sen. Barack Obama is the inevitable Democratic nominee, sparking a flow of superdelegates to his side.

The Clinton campaign, however, argues that a 2 to 5 point win would be enough to carry her forward, in spite of pundit prognostications.

If Sen. Clinton wins with a margin of two to five percentage points in Pennsylvania, the campaign says, it would play up the victory and continue. But pundits say such a showing could weaken fund raising and the campaign’s argument to superdelegates that Sen. Clinton is the best candidate to win in big swing states in a general election.

Claire McCaskill, freshman Senator from Missouri and Obama backer thinks the Land of Lincoln Senator will lose Pennsylvania by double digits.

Usually, this means the campaign believes it will lose by something less than double digits.

How to win by losing — lower the expectations for your performance.  When you over perform to your expectations, you win.  Expect a lot of this expectation setting by both sides.