That's a whole lot of undecideds a month out. Still, not good for Bredesen if he ultimately wants to win.
You could argue the same for Blackburn. This is a Trump +26 state where his approval is only +7, and she can barely consolidate 42% of the R-leaning electorate right now.
Which means that toward the end they will break for Blackburn. Count on it. In order for Democrats to win in deep red states, they need to be pushing very close to 50 and tied if not a little ahead. We've seen this before with Kansas and Georgia in 2014. Democrats leading in polls but on election day lose anywhere from 3-10 points.
Maybe the underperformance of Democrats will lessen somewhat because of the nature of the cycle. Maybe it has nothing to do with the electorate and more with poor campaigning?
Undecideds in Southern States aside from FL pretty much always break R at the end though. Even if it doesn't show up in the polling super-well, the D still under performs whatever the media expected them to do. Only exception off the top of my head is VA-GOV 2017, if that even counts as a 'real' southern state anymore.