Bevin will probably win by that margin next year. This year should have made it clear that Kentucky will not be voting Democratic any time soon. I expect Republicans to gain complete control of all the statewide offices in the next few years there. McConnell also, is absolutely safe in 2020, and will win by double digits.
How exactly?
Maybe because a Democrat who was a "strong candidate" lost to a "weak incumbent" Republican in a district that's significantly more Democratic than Kentucky as a whole in a great year for Democrats?
Exactly. Beshear will probably come within single digits, but I don't expect for him to get any closer than that. And it's entirely possible that Bevin wins by low to mid double digits, like Blackburn did in Tennessee.