Team Mitch has weathered tough elections basically every time since he first won (except for like one year). It's a midterm year during an unpopular President's sixth year. The GOP has a chance at winning the Senate. The national climate favors the incumbent's party. It's Kentucky.
Mitch isn't going to lose. It won't even be particularly close in the end.
I'm not sure how you can believe it won't be close. Look at the numbers. I could see Grimes losing by 6 if it gets out of hand for her, but honestly this has been neck and neck and will continue to be so. The only reason Rand Paul got a relatively health double digit margin against a statewide officer is because Conway fumbled the ball so poorly.