If a television or radio station determines that a political ad is false, should it refuse to run the ad?
That's exactly what the nonpartisan group Free Press is calling on stations to do.
"They certainly could reject some of them," said Matt Wood, the group's policy director.
At the very least, they could do more fact checking, he said.
Free Press's new report, Left in the Dark, analyzes political ads in several swing-state markets: Charlotte, N.C.; Cleveland; Las Vegas; Milwaukee; and Tampa, Fla.
It says viewers are seeing more political ads than ever before, but television stations only rarely fact check any of the ads. And even when television stations conduct fact checks, that story is overwhelmed by a flood of TV ads. In Denver, there was one minute of fact checking for every 162 minutes of campaign ads.
"What they owe the public is to point out the discrepancy between how many times they run the ad versus how many times they report on its veracity," Wood said.
Stations often say they are required by federal law to run campaign ads without censorship. That's largely true for candidate ads.
One extreme example of a candidate ad is one run for an obscure Democratic candidate challenging Rep. Keith Ellison, D-Minn., who is a Muslim. The challenger's ads feature images of beheading and dead fetuses.
The station said it was required to air them. The federal law says the station "shall have no power of censorship over the material broadcast by any such candidate." But superPAC ads have no such protection.
"There's a difference between candidate ads, which stations pretty much have to run, and third-party and superPAC ads, which they could reject," Wood said.
It happens occasionally. This month in Iowa, several stations refused to air an ad by the Humane Society Legislative Fund against Rep. Steve King, a Republican.
The ad implied King opposed a ban on children at dogfights. (He says he voted against the bill because it should be a state, not federal, issue.)
But the Free Press study found that stations almost never rejected these third-party and superPAC ads — and few of them were engaging in serious fact checking.
One exception is in Tampa, where WTSP and the Pulitzer Prize-winning PolitiFact website have joined forces. In one recent segment, an ad from Americans for Prosperity received PolitiFact's worst rating.
"We gave it 'Pants on Fire,' because it's so misleading, and it's ridiculously false," said Angie Holan of PolitiFact Florida.
But that didn't stop WTSP from airing Americans for Prosperity ads 150 times that month, Free Press reports.
"If the station's own news team says it is false, and they keep running it, you have to question the station's commitment to the audience," Wood said.
Tracie Powell, a reporter with the Poynter Institute's Sense-Making Project, says it isn't hard to guess why TV stations are airing these questionable ads.
"TV stations have been hit hard, so they're less likely to turn down paid advertising these days," she said.
But that doesn't relieve them of their responsibility to serve the public, Powell said.
"We have an obligation to tell viewers what's true in the ads and what's not true," she said. "Unfortunately, that's not happening at a lot of stations."
She says that makes it even more important for voters to educate themselves. She uses the Ad Hawk app from the Sunlight Foundation, which allows you to hold your smartphone up to a campaign ad and get information about who's behind it.
Scott Finn is news director at member station WUSF Public Media in Tampa.