The narrator claims that outside groups attacking McCaskill want to end Medicare, cut student loans and expand oil subsidies.

The ad mirrors another 30-second spot McCaskill released in February portraying the groups that are attacking as out-of-state interest groups with no business meddling in Missouri's elections.

Taken in concert, the two ads suggest a strategy for lessening the blow of attacks as conservatives work to oust McCaskill, one of the most vulnerable Democrats up for reelection in 2012.

McCaskill knows the attacks from groups like Crossroads and the U.S. Chamber of Commerce will keep coming. So she and her team are focusing their efforts on undercutting the credibility of those groups in the eyes of Missouri voters.

"I'm getting all the name brands. I think I'm at the top of a lot of folks' lists, and I'm really trying to turn it," McCaskill told MSNBC in April. "If you don't know who's paying for it, don't believe a word of it."

Lloyd Smith, who heads the state GOP in Missouri, called the ad another example of McCaskill refusing to practice what she preaches.

"McCaskill is criticizing ads exposing her record of voting in lockstep with Barack ObamaBarack Hussein ObamaDems flip New York state seat that Republicans have held for nearly four decades Trump denies clemency to 180 people Mellman: Memories may be beautiful, yet… MORE, but she has remained silent as her liberal allies and special interests pour secret money into Missouri on her behalf," Smith said in a statement. "As McCaskill herself has said, ‘Don’t take anyone seriously that says one thing and does another.’"

 McCaskill's strategy is similar to that used by President Obama in an ad his reelection campaign released in April, warning voters not to take seriously attack ads from groups associated with the oil industry, such as Americans for Prosperity, which was on the air criticizing Obama's energy policy.

"So when you see this ad, remember who paid for it — and what they want," said the Obama ad.

Watch McCaskill's ad:

- This post was updated at 3:49 p.m.