Lexington sums up an argument, coming from various quarters, on the consequences of the GOP doing well today:
It could make it harder for Mr Obama to get his agenda through the Senate. Democrats from red and purple states are nervous enough already. If they think voters are recoiling from Mr Obama's policies, their support for him will grow more guarded and conditional.
[The 2009 races will] determine whether Democrats believe they'll be punished or rewarded for favoring an Obama-identified health care plan.
Megan makes the same point:
Either Hoffman will lose, in which case the strategy of policing the party will lose some of its appeal, or he will win, in which case Blue Dog democrats and Republicans in squishy states will probably tack right--a critical win during the health care debate.