I think one of the most interesting political stories to watch in 2010 is going to be whether the trio of Democratic Senators who already have disapproval ratings over 50%- Chris Dodd, Blanche Lincoln, and Harry Reid- can actually get voters to change their minds about them.
Most of the time when we put out a poll for a politician who has a low approval rating a big part of it is a high level of ambivalence toward them, which is troublesome but much easier to overcome than avid dislike. It's a lot more possible to turn 'eh' feelings into votes than 'ugh' ones.
Jon Corzine's failure to get reelected showed that you can only get people who dislike you to vote for you to a certain point so for Democrats to keep these seats they're either going to need to be able to get voters to change their feelings about Dodd, Lincoln, and Reid- or run other candidates.
Politics is full of surprises and who knows what unexpected things will happen in the next year but if I had to pick three Senators running for reelection right now who will be cleaning out their offices at this time next year it would be Dodd, Lincoln, and Reid. Once voters have decided the disapprove of you it's very hard to overcome that.