The excellent Wisconsin Advertising Project, which monitors political advertising, released a big report this week on spending in the battleground states of the presidential race. It had several big findings of note to the politically obsessed, including the fact that the McCain’s advertising during the week studied (Sept. 28-Oct. 4) was 100 percent negative, compared with 34 percent for the Obama campaign.

But there was also one less-noticed fact that helps explain why McCain may remain within striking distance in Minnesota.

To cut to the chase on that last point, check out the comparison of McCain and Obama ad spending state by state in the 15 where both campaigns were buying local advertising. Minnesota is one of only two states where McCain has been outspending Obama, and his Minnesota spending has been five times greater than Obama’s. (The other state where McCain spent more last week was Iowa, but the difference was negligible.)

Advertising Spending by State 9/28 - 10/4

Several things jump out: Obama is absolutely crushing McCain overall in battleground state spending. I assume that’s because he has that much more money, which directly relates to his controversial (and hypocritical) decision to drop out of the public financing system.

In North Carolina, Obama is outspending McCain by more than eightfold. In Virginia, by almost fourfold. In Missouri, more than double. In Florida, more than triple. All of these are states that went Republican in the last election and Obama appears to be ahead in all of them except Missouri.

Most analysts have attributed Obama’s surge in the polls to the financial crisis (which they presume is favorable issue ground for Obama) and to other factors. But one thing I’ve noticed, because of my obsession with the electoral vote map, is that Obama’s surge has been stronger in the swing states than it has nationwide. One factor must be that he is clobberizing McCain in ad spending in the swing states.

Except Minnesota. It seems likely to me that the McCain’s national strategists at some point chose Minnesota as one blue-leaning-but-contested state in which to play offense and try to force Obama to play defense. (Just today, for example, McCain is back in Minnesota, his fifth visit this year.)

Obama’s national ad buyers have apparently decided not to take the bait. Look at the list, Obama has spent less in Minnesota than in any other battleground state. They must have some combination of confidence that they can win Minnesota without much advertising (Democrats had a tremendous turnout operation for Kerry in 2004, and the Obama campaign is run by the estimable Jeff Blodgett), or the belief that even if they were to lose Minnesota, it would be quite survivable if they can take away such traditional red states as North Carolina, Virginia, Colorado and Missouri, not to mention the biggest swing states: Florida and Ohio. And the electoral math certainly backs up that idea.

The other thing that is most notable, as pointed out by Ken Goldstein of the University of Wisconsin, who runs the Wisconsin Advertising Project, is that the race is being fought mostly on red territory. The states where both campaigns are advertising this close to the election is the best possible shortcut to the states that they believe are in play.

Ten of the 15 states went for Bush in 2004. As measured by the trend line calculated by Pollster.com, Obama is currently ahead in 13 of the 15 states. McCain leads in Indiana and Missouri, but both are currently rated as toss-ups.