Candidates tend to over-perform the polls in safe states, and I would expect the same here, especially considering how polls out of Appalachia underestimate republicans. Most of those undecideds will probably go for Trump.
While this is true to some extent, the 2016 result there was Trump 61, Clinton 35. This poll has Biden already at 36 even with 11% undecided. Quite possible that Biden ends up in the upper 30s here and that the state SLIGHTLY swings D. Biden's a less terrible fit for this part of the country than Hillary Clinton is. (I'm not saying much, but TN might be Trump by 22 or 23 rather than Trump by 26, and that this poll would back that up)
