Somehow Trump's national numbers seem to consistently be better than the % of the vote he actually gets in states.
The polls could be sampling a bunch of people who never actually bother to show up to vote. In other words, Trump supporters may be slackers (or else non-Trump voters may simply be especially motivated).
Another explanation is that when people are actually faced with the option of voting for Trump in the voting booth, some of them don't go through with it. But then a few weeks later, they go back to supporting Trump.
