Leahy's call for Clinton to bow out is just an opening shot. The grumbling has been getting louder and louder over the last few weeks. First it's behind the scene mutterings, then it's anonymous leaks to the press, then it's some veiled comments from Richardson, and now the first Senator makes an on the record comment.
Yes, he's an Obama supporter and is only one Senator, but it's a big step to make to tell another Senator to withdraw.
Right now, Clinton has a lot of power. She has the chip of withdrawing peacefully and she can cash that in for something important, maybe the VP slot, maybe the majority leader position, maybe her pick of committees to chair, whatever she wants. With time though, that's going to fade.
If she waits until the end, then what does she have left? If she lets this drag on until the convention and she doesn't win, her seat could become worthless. If Obama loses in part due to the fight, what are the odds that her earmarks get voted on favorably? What committee seats will she be given? If she waits until she's forced out, there will be a backlash among Clinton supporters against Obama, and that will create a second backlash against her from people who didn't want to be put in that role.
Yes, right now she has a chance of the Presidency. With 10% odds of getting the nomination (and fading with every Superdelegate who commits), and - at best - a 40% chance of winning the election if it's done through a convention fight, she has - at best- a 1 in 25 chance of winning the White House.
She's risking a lot here. I would have accepted a deal by now, but that's one of the reasons why I'd never be in this position in the first place.