David Gergen actually said...

If he were to lose Pennsylvania, that's curtains. I think he would withdraw at that point.

I think so, unless he unexpectedly collapses or has a heart attack.

If Rick Santorum wins, he has a very strong argument that this ought to be a one-on-one with Romney.

I think Romney will probably lose the states. Mitt Romney faces the prospect he's going to lose a few states here in the next few weeks.