The placement of the ads, combined with their tone and message, gives a great idea of exactly where each campaign thinks it will win.
The Donnelly campaign targeted stay-at-home moms at the start of the month with an ad featuring Donnelly's wife, Jill, which ran during daytime television, including soap operas. The following week, Donnelly hit the same audience with a tougher piece featuring Republican vice presidential pick Paul Ryan denouncing Richard Mourdock's beliefs about compromise.
Mourdock hit back the next week with a play to political thought leaders, airing an ad during the Sunday morning talk shows that answered the classic political question, "Are you better off today than you were four years ago?" In it, he said Donnelly and Obama "made things worse."
The strategy is complicated, and hardly uniform, although buyers have a few basics they stand by, all designed to hit likely voters. Morning and evening newscasts get bought up first because viewers tend to be more likely to vote. Then come daytime shows and primetime hits.
Buyers can check demographic reports to target spots, but they will just as likely spend on primetime crime dramas that reach large numbers of voters over the age of 50. Crime shows like CSI have been shown to not only reach older voters, but to reach older women who are more likely to vote than men.
Experian Marketing tested last month which shows break through to which political subtypes. Some shows fit an obvious political persuasion: "Super Democrats" love "The Daily Show with Jon Stewart," while "Ultra Conservatives" named "College Football Regular Season" on ESPN their favorite program.
Further to the middle, "mild Republicans" picked mostly reality shows on cable stations and "on the fence Liberals" opted for adult cartoons like "Aqua Teen Hunger Force" and "American Dad."
Bill Perkins, a veteran Republican ad buyer based out of Indiana, notes that many social media consultants have flooded Washington this election season with promises of micro-targeting voters far beyond any television ad's capabilities.
But that theory has not been thoroughly tested yet, and campaigns are still placing their money and their trust in television, he said.
Spending in Indiana's Senate battle backs up Perkins' assessment. Mourdock and his supporters will have spent $2.9 million on-air by the end of the week, while Donnelly and his friends will have spent $3.3 million. And the explosion of spending by super PACs has even amplified the campaign air war, he noted.
"These guys in Washington have gobs of money to spend and they just don't care that much" about paying for commercials, Perkins said.