The polling could be wrong because turnout on Election Day is different than the mix in the polls. Pollsters have been wrong before and the missed Brexit in the UK, but the polls reflect the best estimate. The polling does have an institutional bias against the "Sailer Strategy," but almost every establishment outfit has this bias. However, I followed the Brexit polling closely and there was a clear trend in favor of Brexit over the long-term because the floor kept rising. If Trump's floor is rising in the polls, that is a sign he is moving in the right direction.
The main concern I have is the ground game. Trump put zero effort into having a ground game in the primaries, he ran a skeleton campaign that pulled up stakes and left after the primary.
In order to win, Trump needs to have a massive ground game that drives his demographic to the polls. If that happens, he wins. If it doesn't, he loses.
Similarly, Clinton has to get all of her key demographics out to vote, but the entire Democrat machine will be working overtime to stop Trump.
Many GOP higher ups, and probably some of the people who fund get-out-the-vote (GOTV), don't want Trump to win.
The Polls Aren’t Skewed: Trump Really Is Losing Badly
Trump Administration open thread - Tell us your thoughts.
40 minutes ago