Broadcast executives in Denver maintain that unless ads contain blatant falsehoods, it is their policy—and even their responsibility—to air political spots by outside spending groups. Michael O’Brien, director of sales for EW Scripps Company, the owner of KMGH, Denver’s second most-watched station, said KMGH requires supporting documentation for claims made in ads by super PACs and nonprofits. In 2010, KUSA pulled an attack ad by a nonprofit that falsely accused the much-maligned Congressman Perlmutter of voting to require health insurers to cover Viagra for convicted sex offenders.

But not one Denver station could recall a single political ad it had rejected in the 2012 elections.

“We’re a business, and we’re also stewards of the public airwaves,” Cornetta said. “Political speech is protected speech. To the degree someone wants to send a message, we believe we have a responsibility to allow them do so.”

When challenges to ads do arise, Cornetta added, it is usually because lawyers representing the target of the ad send a cease-and-desist letter to the station. The station then forwards the complaint to the advertiser, who must either refute the factual challenge or revise the contents. KUSA will not pull a spot without offering an advertiser a chance to respond. “A lot of times it just goes away,” Cornetta said.

Challenges from the stations themselves, meanwhile, seem to be far and few between. By opting for skillful deceptions instead of black-and-white falsehoods, outside spending groups appear to have identified a loophole that neither broadcasters nor the fcc have shown any appetite for closing. Jeff Harris, KMGH’s news director, argues that “Ads are much more sophisticated now. They’ve gotten defensible.”

Free Press, the media watchdog organization, analyzed the political advertising and news coverage of Denver’s four leading broadcast stations in during August and September. Timothy Karr, senior director of strategy for Free Press, contends that the approach most local broadcasters take—waiting for challenges and then demanding proof of blatant falsehoods before pulling an ad—falls short. The stations, he says, need to reject deceptive ads before they hit the air.

EW Scripps’s O’Brien said that a “common tactic” among political advertisers is to make outrageously false claims in the expectation that they will gain wide attention before eventually being taken down. “It’s a shock factor,” he said.

If the corporate side of local television stations were to screen out these falsehoods before they aired, the public might be better served. And if they drew the line at deceptions, and not just at inaccuracies, they might raise the level of political debate a notch.

In the newsroom: Is factchecking the answer?
When the stick-figure ad attacking Perlmutter was released, broadcasters were legally required to accept it, because it belonged to a federal candidate, Joseph Coors.

But two Denver stations gave it additional treatment on the air. KUSA’s “Truth Test” found the ad’s allegation—that Perlmutter was responsible for scamming taxpayers—was “a misleading statement.” KCNC’s edgier “Reality Check” segment declared the ad “DECEPTIVE,” with a bright red stamp. “Bottom line,” announced kcnc’s reporter, Shaun Boyd, “there is no evidence Ed Perlmutter was corrupted by his ex-wife’s lobbying.”

Kathleen Hall Jamieson—the director of the Annenberg Public Policy Center and a crusader for factchecking of political ads—says Denver had the best on-air reality testing in the nation. “There were more stations doing more factchecking than any other market we could find,” she said.

But even in Denver, the factchecking was swamped by the endless barrage. Karr’s Free Press report compared the amount of time spent airing ads by five leading outside spending groups to the time the stations devoted to covering the ads, and found this: Though Denver’s factchecking surpassed all markets Free Press studied, its stations cumulatively aired 162 minutes of advertising by outside groups for each minute they spent covering them.

“Free Press concluded that local news coverage about these political groups did not begin to address the avalanche of misinformation in political ads,” the report declared. Karr contends that although stations could not be expected to match ads that run repeatedly minute for minute, his findings illustrate a serious deficit in the quantity of factchecking and news coverage of political ads and expenditures.

The debate over the adequacy of Denver’s factchecking bears on two key questions facing broadcasters: How frequently and prominently can they reasonably be expected to debunk misleading ads? And what is the effect?

Sasha Chavkin covers political money and influence for CJR's United States Project, our politics and policy desk. He has written for ProPublica, the Center for Public Integrity, and The New York World. Follow him on Twitter @sashachavkin.