It's the sleeper Senate race of Tennessee. The last Democratic wave midterm had a competitive race there between Bob Corker (who won and is now retiring) and Harold Ford, Jr. There was an infamous ad that implied a white girl was having sex with Harold Ford, Jr (who is black) and Corker won, but it was close. This time around the Democrats are running a very popular former Governor who is white. It's not likely that Phil Bredesen can win it, but there's a small chance.
He is more likely to win than O'Rourke at this point. Bredesen actually led some polls, O'Rourke just led one by two points.