From what I understand, Santorum is going to endorse romney, and the polls on the subject always said, if Santorum dropped out, half and half split of his votes between Mitt and Newt. But the one unknown is, how angry his supporters will be because of him endorsing Romney, that has never been polled.
One half of Santorum's polling is 12-15%, and that would at least give Newt a big bump..
50% of Santorum turns this into a blowout for Romney. Newt needs to do better than that. I have a sneaking suspicion a large number of those supporters will sit it out now rather than vote for either of the candidates who trashed the one they were supporting. Perhaps if Santorum endorses Romney, some might get angry enough. Hopefully, Santorum will either not endorse or will support Gingrich.