Dems have gone after DeLay only after figuring out that GWB is our tar baby...they wasted tremendous energy, money, and political capital going after Bush (even after the election).
Weakened from their efforts against our tar baby, they're only now really going after smaller game (and they'll still fail).
Devoid of new and popular ideas, Democrats can only hope for (or engineer) a scandal against Republicans. It's all that they've got.