I’m late to this, but The Washington Post’s Paul Farhi had a sharp piece the other day about the uses and limits of campaign ads in presidential elections.

Farhi gets to the main point right at the outset:

But for all of the cash thrown at presidential TV ads—perhaps more than $1 billion between now and November—their impact has historically been relatively small in swaying large swaths of voters in the general election.

“The most fundamental point about political advertising is that it matters at the margins,” said Erika Franklin Fowler, director of the Wesleyan Media Project, which tracks and analyzes campaign ads. “It might help in a close election,” but factors such as the state of the economy and partisan identification are much more influential, she said.

That doesn’t mean that the campaigns are irrational to spend so much time raising and spending money on TV. As Al Gore could tell you, in the right circumstances marginal effects can make a big difference. What’s more, the findings of limited impact are based on rough parity between campaigns. There’s a reason that, as one expert tells the Post, “No one is willing to unilaterally disarm.”

But it’s worth keeping in mind, as we look slack-jawed at the sums being tossed around, just how inefficient the ad onslaught typically is. Later, Farhi writes:

Campaign media advisers say that waging a modern presidential ad campaign is like swinging a giant hammer at a penny nail. Almost all of the commercials are aimed at a minority of a minority of voters: the few who haven’t yet made up their minds in a handful of battleground states. A Gallup poll of likely voters in 12 such swing states in early May found that only 7 percent described themselves as undecided. And the number shrinks the closer it gets to Election Day.

Of course, that applies to the general presidential election, where voters are guided by partisan attachments and have many other sources of information about the candidates. Farhi smartly notes that political ads can play a bigger role in primary contests, in part because the disparity between rival campaigns can be far larger. (The Restore Our Future blitzkrieg wasn’t the only reason Mitt Romney prevailed in this year’s Republican contest, but it didn’t hurt.)

Meanwhile, as CJR has previously noted, if a deep-pocketed campaign donor really wants to have an impact, he’s got better odds if he directs his cash to lower-profile races, where it can command a far greater share of the total information environment. Which is, in turn, another reason for newsrooms to shift campaign journalists off of presidential gaffe patrol and to down-ballot races and other stories instead.

(H/t The Monkey Cage, via Twitter)

Greg Marx is a CJR staff writer. Follow him on Twitter @gregamarx.