barack-obama-at-central-high.jpgHENDERSON, Nev. (AP) _ President Barack Obama's campaign is stepping up criticism of rival Mitt Romney's past investments in China.

In a new television ad, the campaign accuses the Republican nominee of investing in a company that maximized profits by paying Chinese workers “next to nothing'' to manufacture appliances.

The ad aims to discredit Romney's assertion that he would take on China's trade advantage over the U.S.

The narrator says, quote, “Mitt Romney, tough on China? Since when?''

China has emerged as a key economic issue in the election. Romney is running ads saying Obama has been too soft on China and let U.S. jobs move overseas. Both campaigns see the issue as an appeal to undecided working-class voters.

The ad is running in New Hampshire, Virginia, Florida, Ohio, Iowa, Colorado and Nevada.