[cnn-photo-caption image= http://i2.cdn.turner.com/cnn/2008/images/10/08/art.mccainadprez.cnn.jpg caption="A McCain ad calls Obama 'not presidential."] WASHINGTON (CNN) - The race for the White House is being waged in the final weeks in American living rooms through a blitz of negative campaign commercials.
And though Sen. Barack Obama's campaign circulated a University of Wisconsin Advertising Project study earlier this week indicating all of Sen. John McCain's ads are negative compared to just 34 percent of Obama's, both campaigns are spending about equal amounts on attack ads.
An analysis of campaign commercials aired over the last seven days shows Obama outspent McCain nationwide by more than 2-1: $21.5 million vs. $9.2 million.
Watch: Negative ads dominate the campaign homestretch
But just under half of the money Obama is spending is going toward negative spots, meaning the Illinois senator is roughly keeping pace with his GOP rival when it comes to negative commercials, in terms of cash spent.
Campaign Media Analysis Group's Evan Tracey, CNN's consultant on campaign advertising, said Obama's cash advantage over McCain provides the Illinois senator with a luxury McCain cannot afford: the means to run both positive and negative TV spots.
"McCain is almost all negative because he needs to be," Tracey said, adding that McCain is "behind in the polls and outgunned."