The national Democratic brand is not very good in Texas. And that means even in the increasingly unlikely circumstance that there's a special election to fill Kay Bailey Hutchison's seat in the Senate, Republicans should be at a pretty strong advantage.
61% of voters in the state disapprove of Barack Obama to 33% who like the job he's doing. He's still pretty popular with Democrats- 75% approve- but only 4% of Republicans give him good marks and independents are aligned against him by a 70/19 margin. Those are the worst numbers on Obama PPP has found with them in any state.
Obama's actually a lot more popular than Congressional Democrats- 66% of Texans disapprove of them to only 24% happy with their performance.
What it all adds up to is voters saying by a 53-38 margin that they would choose a Republican over a Democrat to replace Hutchison in the Senate. That's due largely to a 55-22 GOP advantage with independents. Candidates matter and if there does end up being an election John Sharp may prove to be superior to the 'generic Democrat' but in this political climate I don't know that Texas is somewhere Dems are going to be able to play effective offense.
Full results here