The other obvious search words involve search terms people use when researching specific issues. Here again, McCain is busy; his people say that at various times they've bought 10,000 different words. But other candidates are active, too, sometimes appearing in surprising places. Who shows up when you type in "stop global warming"? Bill Richardson! Giuliani pops up with "flat tax" and "illegal immigrant." But when I tried "universal health care," nothing from any candidate came up. Vary it a little by typing "health care reform" and you get a paid link to … John McCain. (On the other hand, in my experience, typing in "Fred Thompson" often leads to sites selling authorized campaign merchandise, as if the politician-actor were running on eBay.)

As this medium evolves, you can expect dirty tricks like "click fraud," which is the practice of methodically clicking on an ad link to drain the advertiser's kitty. And then there's the question of negative search ads. The search companies have standards for ad content, but it's unclear how this is applied to political speech. Can you place an ad calling someone a crook? An adulterer? A liar?

Before we resolve those questions, the political action will likely spread to social networks, where advertisers can target users by their personal interests and political affiliation. "I can see targeting conservative Facebook users in South Carolina who have guns," says Republican political consultant David All. Next time around: the Facebook election.

With Jennifer Ordoñez

With Jennifer Ordo�ez

© 2007