The campaigns do not rely on the publicly available poll data for the reasons you pointed out - they need accurate polling in order to make serious decisions ab

The campaigns do not rely on the publicly available poll data for the reasons you pointed out - they need accurate polling in order to make serious decisions about resources. They pay polling companies to get accurate polls and they keep this data private. The publicly available polls are done for free by polling companies or by news organizations. Unfortunately some of these companies apparently have an agenda to push. So they skew their sample away from what the likely voters are to get the result they want for propaganda purposes. I think that the rise of Nate Silver has ironically made this situation worse. He advocates taking an average of polls to get a true view of the situation. So if you are skewing you poll to get a certain outcome and you know the poll will be averaged, you need to warp your results even further. Ok, disclaimer time - I don't have any inside knowledge or real evidence of any of the above. It does seem to fit however. I can't explain why it seems all the distorting is to make the Dems lead seem bigger than it is - that is, why aren't there pollers on the other side of the aisle doing the same thing? So you'll have to decide for yourself if there is any merit to the above theory.