Tennessee is what Tennessee is. Nothing shocks me about this poll given the fundamentals of this state, which veered further right in 2016. This state shouldn't be competitive except in a massive "blue wave" scenario.
Presumably this is a double-whammy Kavanaugh event: a combination of usual GOP/leaners reflexively rallying to Blackburn's side over the "mistreatment" angle and a bunch of disgruntled Democrats protest-polling because of his proclaimed support for Bart.
However, that also means that this could reside (as TN Democrats aren't going to vote against him when push comes to shove, and GOP/leaners have no reason to be mad at Bredesen over it).
