American Crossroads, a non-profit group known as a superPAC, made an $8.3-million buy for ads that feature small business owners blasting Obama's "bad decisions" on job creation. The series will run in Colorado, Florida, Iowa, North Carolina, New Hampshire, Nevada, Ohio and Virginia.

"With Barack Obama calling the shots in the White House, entrepreneurs feel threatened and admit they are uncertain of their ability to create jobs," said American Crossroads media relations director Nate Hodson.

"President Obama would rather make small business owners the enemy than take responsibility for mismanaging the economy over the last four years."

Crossroads GPS, an affiliated group that is not required to reveal donors, launched a separate, $2.3 million ad buy in four states, targeting Democratic lawmakers in Montana, Nevada, North Dakota, Wisconsin, and New York.

Obama and Romney are locked in a bitter battle for the White House, and the 2012 campaign has been flooded with hundreds of millions of dollars in political advertising, largely negative.