It is very difficult to poll in a electorate which is so diverse and is changing rapidly. They made changes in the weighing of votes from last time due to the massive difference in college education and voting behaviour, but things change. Trump has had gains in Latino and Black votes, which to a outsider seems baffling. There is probably quite a lot of the voters who would not want to admit they vote Trump as it is seen as so controversial (to put it mildly)l, but then vote for him in the election. What is clear is that the Democrats will again win the popular vote and have only failed to do so once this century. It is the baffling voting system which is increasingly favouring Republicans.