This site has had a ban on listing internal polls for some time now. The logic behind this is that when a candidate for office commissions a poll, he is only liable to leak its results to the public if it contains good news for him, thereby encouraging donors, press persons, etc. This does not mean per se that the poll is "biased" -- many pollsters do very good and thorough work on behalf of campaigns and affiliated interest groups. But it does mean that there may be a bias in which information becomes part of the public record: we learn about a poll that has a candidate ahead by 10 points in a state, but not one where he is down by 2. For this reason, such polls have been excluded.
There have been an increasing number of surveys, however, particularly on the Senate side of things, that somewhat test our definition of an "internal poll". Where would you draw the line on the following spectrum?
1. Polls commissioned by the candidate himself.
2. Polls commissioned by another candidate for office in that state.
3. Polls conducted by a national campaign committee (e.g. RNC, DSCC)
4. Polls conducted by an interest group (Emily's List, US Chamber of Commerce), but formally unassociated with the candidate.
5. Polls that are private, but conducted on behalf of someone with no direct interest in the campaign, such as an outside lobbying group.
Presently, I have been drawing the line between #3 and #4. But I'm not sure that there's a major philosophical difference between, for instance, Emily's List commissioning a poll, and the DNC doing so. I'm also not so sure that I necessarily have things in the right order.
Anyway, I've come to very much trust in the wisdom of the 538 crowd -- so opinions are solicited and appreciated.