Romney's campaign has ramped up more recently, airing ads that mostly criticize Obama rather than promoting the GOP presidential hopeful. Romney's campaign received a big assist earlier this month from Americans For Prosperity, an independent group backed by the billionaire brothers Charles and David Koch, which launched a $25 million ad campaign featuring voters who supported Obama in 2008 but plan to vote against him this time.
No state has seen more advertising than Ohio, where Obama and Republicans have spent nearly $100 million to date. Florida places a close second, while Virginia is third.
Wilner said that despite the Republican cash advantage going into the fall, the level of ad saturation in the battleground states thus far may make it difficult for Romney and his allies to gain significant new traction.
"For Obama, summer time may have proven to be a better time to get a message across than in the fall. Republicans are hoping sheer tonnage of ads will be enough to convince voters not to give another term," Wilner said.
Follow Beth Fouhy on Twitter at www.twitter.com/bfouhy
Copyright 2012 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.