Barr ran the third closest Congressional race in the country two years ago. On Election night, the NRCC sent out emails to its volunteer lawyer network in anticipation of a recount. The margin, 647, just wasn't close enough.
The challenge for Barr is that Ben Chandler has voted to the right of the Democratic caucus. It is therefore harder to motivate conservatives from outside the district to donte than they would be inclined to donate to defeat John Yarmuth, for example.
But that's where realism comes in. No matter how much Yarmuth annoys conservatives, his advantage in registration makes Kentucky 3 a bad value for Republican donations. In Kentucky 6, however, we have a real shot.