(CNN) - An independent, conservative group spent $1.2 million on a new television ad targeting Rep. Tammy Baldwin, the Democratic candidate in the heated Wisconsin Senate battle.
The commercial, made by Crossroads GPS, will run on local and broadcast networks in the Badger State beginning Wednesday.
"Tammy Baldwin's tax and spending agenda is just too extreme for Wisconsin," the ad's narrator says.
The commercial slugs Baldwin, a seven-term U.S. congresswoman, for "rubber stamping" legislation passed when Democrats had control of Congress during President Barack Obama's first two years in the White House. The ad mentions the so-called Wall Street bailout, health care reform and the American Recovery and Reinvestment Act, also known as the stimulus bill.
"We just can't afford Tammy Baldwin's tax-and-spend rubber stamp in Washington," the narrator says.
Her campaign responded to the ad Wednesday, saying the Karl Rove-backed group was wasting its money on the race.
"Despite spending over $6 million attacking Tammy Baldwin this year, all the public polls show we are moving in the right direction. The fact that Karl Rove spent one million dollars attacking us last week and another one million dollars this week, proves that point," John Kraus, the campaign's communications director, said in a statement.
Baldwin is running against former Wisconsin Gov. Tommy Thompson, who captured the GOP nomination in a crowded primary last month.
An NBC/WSJ/Marist poll released Thursday indicated Baldwin slightly ahead of Thompson, 48%-46%. The margin was well within the survey's sampling error. Two days earlier, however, a separate Marquette University poll showed Baldwin leading by nine points.
Thompson attributed the wide margin to Mitt Romney's negative headlines. At the time the poll was released, the Republican presidential nominee was playing defense on secretly recorded footage that showed him making controversial comments at a fund-raiser.
"The presidential thing is bound to have an impact on every election," Thompson told Madison television station WKOW last week. "You know, whether you're a Democrat or Republican. If you're a standard-bearer for the presidency is not doing well, it's going to reflect on the down ballot."
A CNN Poll of Polls which averaged the three non-partisan, live operator surveys that were conducted earlier this month indicated the president with an 11-point lead over Romney in the presidential race in Wisconsin.
The Wisconsin Senate race has been a prime contest on Crossroads' radar, as the conservative group co-founded by Karl Rove has aired several commercials in the state, hoping the GOP can grab the open seat currently held by retiring Sen. Herb Kohl, a Democrat, and retake the Senate majority.
Political handicapper Stuart Rothenberg labels the race as a "toss up/tilt Republican," while another analyst, Charlie Cook, rates the contest as a pure "toss-up."
- CNN's Peter Hamby and Paul Steinhauser contributed to this report.