This isn't a normal year. The primary was a 10 month non-stop media tsunami, how many undecided voters do you really think are out there? If anyone hasn't decided if they're voting for Trump by now then they've been living under a rock.
Given his opponents weakness he has a chance but there likely aren't that many "undecideds" to rally.
what if he stops receiving so much negative coverage? albeit mostly deserved to date
what if he begins to act "more presidential" (using that expression is laughable since HC is his opponent, but I know how minds are molded)
what if suburban turnout increases and urban turnout decreases? (see 2010 and 2014)
it doesn't take a miracle, it takes a tweak here or there
most people writing him off now have been writing him off a long time , so no real surprises to speak of
same ole same ole