If the polls end up being "off", then I think it's far more likely to happen because the pollsters did a bad job of constructing their samples that because the poll respondents were untruthful about who they supported.
This is anecdotal, but I wonder sometimes about if it might represent something bigger in constructing samples:
My aunt lives in Virginia and is a devoutly religious person, and a fiercely loyal Republican. But she's not going to be able to bring herself to vote for Trump. Just can't do it. It seems to me likely that people like her, discouraged voters, not ones who have flipped to the other side, are likely to be underrepresented in surveys. I wonder if the demographic weightings have tended to overrepresent Trump support among evangelicals because the evangelicals who respond are those who aren't discouraged this year.
