This Race reminds me a lot of the North Carolina Race in 2014 between Hagan and Tillis. Hagan had a consistent 1-3 Point lead on Average throughout the Campaign and got pipped in the end.
AZ is huge Vote by mail state. probably 80% of this election will be by mail. All ballots will be mailed Tuesday, so McSally doesnt really have until "the end" to get ahead because "the end" in AZ is about 2 weeks after ballots are mailed when the majority of them have been returned.
I wonder if this is why Hillary did better than expected in AZ, particularly when compared to the nation as a whole. Because most ballots were returned before the Comey letter.