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.
Both Sens. John McCain and Barack Obama are throwing large amounts of money into TV ad campaigns this year.
And though Sen. Barack Obama's campaign circulated a University of Wisconsin Advertising Project study earlier this week indicating that nearly 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.
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. Watch more on McCain's ad attack »
"McCain is almost all negative because he needs to be," Tracey said, adding that McCain is "behind in the polls and outgunned."
"He can't afford the positive ads Obama can. ... It's not likely McCain can raise his own positives with only weeks left but he can raise Obama's negatives."
The campaigns' ad spending patterns over the last week also show the two men are each attempting to drive home a vastly different message in the dwindling days of the race.
Obama is directing his heaviest dollars to television spots that attack McCain's health care plan, while the majority of McCain's money is behind ads that portray Obama as an out-of-control tax-and-spender and one who voted against funding troops in Iraq and Afghanistan.
It's all part of a concerted effort from both campaigns to hammer a few dominant messages through the clutter of the 24-hour news cycle, endless campaign skirmishes, and the chattering class.
Tracey said viewership of the ad buy "is what drives home the messages, not the day-to-day stories."
For Obama, that message is health care and the threat he says McCain poses to it, namely that McCain is proposing to "tax health care, not fix it," according to one ad receiving heavy rotation this week.
It's an argument the campaign thinks will resonate with middle-class swing voters uneasy about the country's financial woes and perhaps fearful of their own job security. It's also an issue that has demonstrated particular salience with women voters this election cycle -- the key voting block this year that appeared initially to be drifting towards the GOP ticket after Sarah Palin was named to the No. 2 spot.
Conversely, McCain and the Republican National Committee are invoking themes that were successful in defeating Democratic presidential candidates in past elections, running spots that portray Obama as a significantly left-of-center politician who wants to raise taxes and cut off war funding. Watch an RNC attack ad »
The McCain ad airing the most over the past week is a 30-second spot called "Dangerous" that claims Obama voted to cut off funding for the war and says he is "too risky for America."
Another McCain ad receiving nearly as much play alleges Obama voted to raise taxes in the Senate 94 times and says he's "not truthful" on the issue.
And with just over three weeks to go until voters weigh in, it's likely the tit-for-tat negative ad war won't let up.
"This is what the final leg of this race is about, not getting outdone," Tracey said.