I want to see a Bredesen vs. Blackburn poll before I move it from safe R to likely or leans. I think some people might be discounting Bredesen too soon--after all, Democrats hold two Senate seats right now in states to the right of Tennessee. Not expecting him to win of course; just not ceding the possibility he'd start out well ahead of Blackburn.
He left office with a 72% approval rating. Some people have brought up Linda Lingle or Ted Strickland. They both left office unpopular.
What muddles things in the South is how racially divided the vote has become. We'll see if Doug Jones can maybe build a path across that. Archie Parnell seemed to, but that could just appear to be so due to low turnout.