The McCain campaign has now shifted virtually 100 percent of his national ad spending into negative ads attacking Obama, a detailed breakdown of his ad buys reveals.

By contrast, the Obama campaign is devoting less than half of its overall ad spending to ads attacking McCain. More than half of its spending is going to a spot that doesn't once mention his foe.

I asked Evan Tracey -- who tracks national ad spending for the Campaign Media Analysis Group -- to detail the amounts each campaign is spending on specific different spots. The idea was to gauge the precise degree of the McCain campaign's shift into negative mode amid his slide in the polls, and determine whether the Obama camp was following suit.

The results were striking, and suggest a sharper turn into negative campaigning as time runs low. For one thing, Tracey says, Obama is now outspending McCain by nearly two to one on the air -- Obama is spending $2.4 million per week, and McCain is spending $1.3 million weekly. But on to the breakdowns.

As of October 1 -- three days ago -- the McCain campaign's $1.3 million weekly is being broken down as follows, according to Tracey, who stressed that he himself wasn't labeling the ads either "positive" or "negative":

* Nearly half a million weekly is funding the ad called "Dome," which attacks "Obama and his liberal allies" in Congress for favoring "massive government."

* A shade more than half a million is funding the ad called "Mum," which attacks "Obama and his liberal allies" as "mum on the market crisis."

* Much of the remaining McCain money is funding a spot called "Overseas," which says that "Barack Obama and his liberal allies are to blame" for jobs going overseas. A negligible amount of the remainder is going to a positive spot, the "Original Mavericks" ad.

This is a dramatic shift from the period before he suspended his campaign. At that time, Tracey says, McCain was spending in the neighborhood of half his ad money on the positive "Original Mavericks" ad, and around half on the negative "Dome" spot.

This week, by contrast, "Original Mavericks" ran on Monday only eight times, suggesting that this positive spot is "cycling out of the rotation," as Tracey puts it. "McCain took out the "Mavericks" spot and replaced it with "Mum," Tracey says.

Now let's look at Obama's spending breakdown.

Of his $2.4 million weekly, Tracey says, well over half -- $1.4 million -- is funding the spot called "Real Change," which criticizes the status quo but doesn't mention McCain once.

The remaining million per week is funding a smattering of ads that do attack McCain, on topics like Social Security, health care, and McCain's "fundamentals of the economy" line.

Pretty striking contrast.