Trump will get a lot of Brexit type voters, meaning, folks who usually don’t get polled because they do not normally vote. They aren’t on the rolls according to Nigel Farage who was on Fox Business coverage afterwards with Cavuto.
When the polls calculate likely voters, I think they often count people who have voted in the last few elections. So even if they poll those people, they may be left out of the likely voter tallies.
Figuring out likely voters vs. registered voters is a secret formula in every poll. If a poll is wrong, it’s because they miscalculated that eventual turnout.