The ad will air for a week on broadcast and cable networks and is backed by a $1.2 million buy.
It targets Baldwin for already having "rubber-stamped over a trillion dollars" in spending, including her support for the bank bailout, the stimulus and President Obama's healthcare reform.
The new ad comes as Baldwin has begun to pull ahead in polls, a reversal of fortunes from mid-August, when Republican Tommy Thompson posted consistent leads over the Democrat. And Baldwin has been able to outspend Thompson to go up on the air, as he spent much of his funds battling through a tough primary.
Crossroads GPS, however, seems intent to help Thompson level that playing field to some extent.
Watch the ad: