I just realized that this race is probably the inverse of Florida: Currently popular (former/current) governor running to flip a senate seat. Personal popularity of the challenger makes the race closer than expected, but after time the highly unfavorable (state/national) opposition to their party results in, still coming up a few to several points short in November, although tighter than it every should've been.
Some variances to be sure (e.g. Scott's less personally popular than Bredesen, but has oodles more money), but I suspect both Bredesen and Nelson's final losing results will be similar (with Bredesen having a greater outside chance of going similar routes as Evan Bayh and Ted Strickland, though likely not so disasterous).
Blackburn and Nelson will both probably win.