Any individual poll might put Trump (or Clinton) ahead, but the margin of error is in this case about four or five times the reported lead, so it doesn't mean that Trump is leading. In the poll averages, Clinton is clearly ahead. But, having said that, the gap widened dramatically (to about 9%) after the Democrat Party's National Convention but has since started to close (to about 5%). Add in the uncertainties and the expected result could be as narrow as 45-43 (albeit still in Clinton's favour).
The result is certainly not a foregone conclusion. Trump has, at the moment, less chance of winning, but he is by no means out of it.
As has been pointed out often, though, the US electoral college system is probably stacked against populist candidates with huge support in narrow demographics, so that may scupper Trump even if he ties with Clinton -- or beats her -- in the popular vote.