The only thing is, you should be selective in what you click on. Clicking on an Obama ad when doing a search for homosexuals shacking up and calling themselves married, that’d mean they'd increase their ad buys targeting this ‘effective viewpoint.’
Free abortions, gay marriage, free condoms, medical marijuana - those are key phrases where you click through and like the old Pavlovian hound, you'll get the DNC salting to dump more and more money into that, and change their ads online and in other media to highlight these ‘focus driven viewpoints.’
But that's not all the places you troll for Obama ads. While the national campaign is kinda a joke, the state campaigns for senate and house seats are a completely different matter. Just adjust your keywords to include the name of a state or the name of a candidate.
And use something like the ‘stealth’ mode in Firefox or incognito in Chrome - that’ll reset your cookies each time you close the browser, meaning you'll be counted as a new visitor next time around.
The best drain on their money, however, comes from searching for Republican keywords - Mitt Romney, tea party, etc. Since they are bidding against Republicans, to get their ads seen, they have to bid higher. Some click throughs can cost them a dime or more, like on a keyword like ‘Sarah Palin’ or ‘Rush Limbaugh.’
Though remember: Only click through on ads on conservative websites. Don't go clicking ads on the Huffington Post. You'll just make money for liberals running the Huffer, and the tenths of pennies you might cost the DNC won't result in any more targeting. They won't spend all that much extra to preach to their choir.
You are assuming that Google is even charging Obama for the ad space.