In an interactive feature, the National Journal includes spending by two PACs linked to Obama and seven PACs linked to Romney, including fund-raising operations with ties to Karl Rove and the Koch brothers.
Constitution Daily went one step further with the numbers, which show political television ad spending between May 1 and August 6 for those 11 campaign finance sources.
We broke the group of 13 states down to nine states based on two factors: low spending levels in Michigan, Minnesota, Wisconsin, and New Mexico; and a recent campaign analysis from the Kantar/Campaign Media Analysis Group.
All nine states were won by Barack Obama as the Democratic candidate in 2008. It looks like eight of the states are in play, while both campaigns are ignoring Pennsylvania and its 20 electoral votes, apparently assuming those votes will go to the president.
In fact, more TV advertising money has been spent in New Hampshire, with its four electoral votes, than in Pennsylvania.
Breaking down the swing states
Among the eight states, Ohio leads Florida as a recipient of campaign financing, with $56 million, compared with $51 million for the Sunshine State.
TV Ad Spending
Source: National Journal analysis, 5/1-8/6, 11 top financing sources
But despite reports that Romney was outspending Obama by wide margins nationally, the spending numbers show a much-closer contest in the nine states. Obama and his allies were leading TV ad spending from significant sources in four states: Ohio, Colorado, Nevada, and Pennsylvania.
Experts strongly believe the Romney campaign will spend heavily after Labor Day, especially in the eight battleground states that will decide the election.
The current Electoral College map shows 247 electoral votes in the Obama camp, out of 271 votes needed to win the election.
If the Democrats take Ohio and its 18 electoral votes, Obama could win the election by taking just one other battleground state, with the exception of New Hampshire.
Nevada seems to be the state closest to the Obama win column, along with Ohio, based on current polls. The combination of Ohio and Nevada puts Obama exactly at 271 electoral votes, just enough to win reelection.
If Romney can take Ohio and Florida, then the reelection path for the president becomes harder, but not impossible.
So any of eight battleground states could put Obama or Romney over the top in the election, if the GOP can take Ohio and Florida.
Fittingly, cities like Cleveland and Orlando have already been bombarded with political ads on television.
The Obama campaign has outspent Romney and two allies (Karl Rove's Crossroads GPS and the Romney-linked Restore Our Future super PAC) in Ohio.
In Florida, groups like Priorities USA Action (the Democratic version of Crossroads GPS) and Planned Parenthood are in the battle for Obama, while the super PAC Americans for Prosperity, with links to billionaires Charles and David Koch, are on the GOP's side.
The significance of the smaller, key battleground states hasn't gone unnoticed by the super PACs, which may raise and spend unlimited amounts of money, including from corporations and unions, in part enabled by the Supreme Court's 2010 Citizens United decision.
Crossroads GPS dropped $1.19 million last week on TV ads in Nevada and $1.3 million in Iowa.
Rove's SuperPAC also outspent the Obama campaign in Florida last week, with $2.3 million in TV ad buys, compared with $1.6 million for the Obama campaign.
An Associated Press analysis of the TV ad blitz showed despite the heavy presence of ads in Ohio, Florida, and Iowa, voters might not be swayed, and they may be tuning out the candidates' messages.
New York-based political ad buyer Joseph Mercurio told the AP that the average viewer in a battleground state will see 20 TV ads for the presidential campaign each week.
"The fact that people are being bombarded with ads in these states and the numbers aren't moving means the voters are very set," Mercurio said. "Some sort of massive event would have to happen to shake this up."
A look at composite poll numbers on Real Clear Politics, a political website, don't show much of a shift in campaign polling despite the spending.
For example, there was a 5 point lead for Obama over Romney in Ohio in early May. The current difference in 4.8 percent. In Nevada, Obama's lead was 6 percent in late May, and it know stands at 5.3 percent.