Tonight's results will matter a lot, of course. But only up to a point. It seems quite likely that Hillary will win Ohio and at least come close in Texas, and perhaps win the primary there--but won't run up large margins. Under most of the likely scenarios, it does not sound like she has any intention of folding her tent voluntarily, even though the delegate math will almost certainly remain awful for her.
That's why I think tonight may matter less than the aftermath in the second half of this week. I assume we're going to see a ferocious push by the Obama campaign to create a climate of opinion that demands Hillary's exit. This hint that he's about to unveil 50 more superdelegate endorsements is a preview. So is the fact that Obama has waited to release his February fundraising haul, which is expected to top an astonishing $50 million. Party leaders and liberal pundits are going to start hammering on Hillary to get out.
What's not clear to me is whether her campaign has a persuasive counter argument. Arguing that she's likely to win Pennsylvania only goes so far, given that it probably can't get her out of the delegate hole--and, moreover, that it's six unbelievably long-seeming weeks away. Who will step forward and argue for Hillary's right to stay in the race? (Here's one bright ray of light: A surprising poll saying two-thirds of Democrats want her to stay in.)
The bottom line is that I'm almost less interested in the particulars of what happens tonight than in what cards the two campaigns play later this week. Whoever wins that argument is what will decide whether Hillary survives to fight another day.