There are a couple stories up today about how the Obama campaign is supposedly advertising on Drudge and speculation about how this might enrage Democratic partisans. Now, I don't know anything specifically about this case. We're planning to put in some calls. But at the moment our reporters are tied up working on another story.

However, in the course of building TPM over the last few years I have, quite in spite of myself, become something of an expert on the ins and outs and mechanics of online advertising.

The simple fact is that just because you see candidate X's ad on site Y does not mean that candidate X 'advertised' on that site, in the sense of deciding to do so or necessarily knowing anything about it. These days the vast majority of internet advertising -- especially in the non-MSM world where sites don't have their own in-house ad sales forces -- is done through intermediaries often called 'remnant' ad bureaus.

The advertiser can just say I want my ad to be viewed this many times, or I want it to play in this geographical area or on sites with a certain demographic, etc.

So, just to be clear, maybe the Obama camp has decided to do some advertising on Drudge. I have no idea. But simply seeing an Obama ad show up on Drudge's site does not tell you anything. They might well be as surprised as anyone.