If you recall, last May/June they wrote him off and by convention time in July he had a 5 point lead and was winning many swing state polls. He can do this, but he can't veer off and go an attack gold star families or obsess about mexican judges that get him off message.
Hover your mouse over the last dots in the graph. I get an information box that shows 8/16, N=2551, Clinton at 44.2, Trump at 43.2.