Balderdash. Polls show that half of Santorum's or Gingrich's support would go to Romney if either dropped out. I'm one that prefers Gingrich, but would probably switch to Romney, not Santorum. But just because I prefer Gingrich doesn't mean I'd agree with him if he endorses Santorum. My reaction would be what it always is when a politician I like endorses one I don't. Instead of improving my opinion of the one I didn't like, it just lowers my opinion of the one I did like.
I have a pretty low opinion of both Romney and Santorum. If Newt drops out, it would be a tough decision for me when my state's primary occurs. I'm leaning Romney, but if Santorum chose Gingrich as his VP, that could tip me back towards him, whereas an endorsement by Newt probably wouldn't change my thinking much at all.
Fine, but I doubt that most Gingrich supporters would embrace Romney.