Obama has received much less help from independent groups favoring his candidacy.
Priorities USA Action, a super PAC formed by two former Obama White House staffers, has spent just over $7 million on ads so far, while Planned Parenthood has spent $1.2 million.
Without the same level of cover afforded to Romney by independent groups, the Obama campaign has to balance running a mix of positive and negative ads.
The Obama campaign is advertising in all nine states. While it has spent more money on populous Florida than any other state, its heaviest ad buys relative to population have been in Virginia, North Carolina, Ohio and Iowa.
The Romney campaign has been on the air in just five states so far: Ohio Virginia, North Carolina, Iowa, and New Hampshire. But Crossroads GPS has aired ads on Romney's behalf in the same nine states where Obama is advertising, as is Restore Our Future, a super PAC run by former Romney advisers.
All told, the top 10 advertising markets for the campaigns and super PACs are Norfolk-Portsmouth-Newport News, Va.; Roanoke and Lynchburg, Va.; Greensboro, High Point and Winston-Salem, N.C.; Columbus, Ohio; Raleigh-Durham, N.C.; Richmond-Petersburg, Va., Cedar Rapids, Iowa; Charlotte, N.C.; Cincinnati; and Des Moines, Iowa.
All are in states Obama won in 2008 but where the contest is tight this year.
Beaumont reported from Des Moines, Iowa.
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