As can be seen from yesterday, there are a lot of negatives in Gingrich's background.
I don't think a vote for Romney in this poll should necessarily be misconstrued as a statement about his electability relative to Gingrich's. I also think Romney would stand a better chance at winning than Gingrich, for many reasons, but if I were Obama I'd still rather face Romney. For one thing, it'll be a negative campaign either way, but it's likely to be much nastier with Gingrich than with Romney. (Both ways, since Obama's people will get nasty too, and it depresses turnout.) For another thing, Obama, for all his faults, is an honorable man, and he knows that there's a chance that he might lose either way, and it could have more to do with factors beyond anyone's control than with the candidates. Better to lose to Romney than to lose to Gingrich. Better for all of us. Finally, Obama knows that it is very likely that both chambers will be controlled by the GOP in the next congress. Gingrich with that congress is a more scary proposition for Obama than Romney.
The thing with Gingrich, and negative attacks, they tend to backfire.
Gingrich had a terrible week last week, and much of that was the Bain Capital attack. He launched it.
If I were Obama, I'd love watching Gingrich shooting himself in the foot in mid-October.