Soup Wars!

John McCain and Sarah Palin may be less certain of this truism lately, but negative campaigning sometimes works.

In response to Campbell Soup's ad campaign mocking rival Progresso for using MSG in some of its soups, Progresso owner General Mills announced on Wednesday that it no longer will include the ingredient in any of its 80 soup varieties.

Now the ball is in Campbell's court: the ads it ran were for its line of Select Harvest soups. But, as I noted last week, the company adds MSG to a number of its flagship condensed soups.

"Now that we have publicly confirmed our strategy on this, we don't know if Campbell's will follow us or not," Progresso marketing manager Kyle Duea said in a statement. "We do expect this move to put pressure on Campbell's."