I'm taking this one with a grain of salt. Imagine a hypothetical pollster. Normally, this hypothetical pollster slants hai polls to favor the dem. So in this situation, he would normally release a Registered Voters poll (which favors the dem) and then move the numbers a couple of points toward the dem with sample selection.
Imagine that this same hypothetical pollster wanted HRC as the nominee. He might just release a likely voters poll on the eve of the convention with a couple of points of secret sauce added to McCain.
I can't imagine this would happen in the real world. But it might.
Exactly what I was thinking! But the fact remains that there is serious animosity between Obama supporters and Clinton supporters. After a couple decades of national conventions serving as coronation events, such a switcharoo would be like dropping an atom bomb. The Dems would fracture enough that McCain would win in a landslide.
If Billary was to somehow pull this off the images of riots would haunt Election Day.
Final thought: the easy answer to all these problems is for Obama to make Billary his VP and pollsters like Zogby may be trying to assist in creating the pressure.