Democrats target the Weak... Like Jim Sensenbrenner???

The Democrats are doing what all parties do, targeting opponents they think are vulnerable. 28 Republicans in the House of Reps are being pelted with radio ads because of their votes on the stimulus bill. So why then, are they targeting Jim Sensenbrenner in WI-05!? He has about as safe a district as any Republican in the Midwest. What do you think? Do Democrats on Capitol Hill actually think they can win in Waukesha, or are they just trying to make Jim squirm?