Tom Brokaw, Katie Couric, and David Gregory endorsing presidential candidates: Could it happen? Actually, it already is—though not quite in the way you might imagine.

For decades, scholars have studied and debated the impact of media, both paid and earned, on the decision-making of swing voters.

Earned media—i.e., news—is generally believed to have limited impact, because the types of broadcasts valued by swing voters are unlikely to contain the pointed messages that are more effective at moving minds. Media outlets delivering more one-sided messages, on the other hand—such as FOX News Channel or MSNBC—are watched mainly by people who already have made up their minds.

Meanwhile, paid media, or traditional campaign advertising, can be targeted at swing voters. But messages and messengers with particular partisan or other motives may not have the credibility to alter those voters’ decisions.

What happens, though, when swing voters are confronted by negative messages delivered by credible messengers?

The 2012 presidential contest is only now escalating to the general election phase, and already some of the best known brands in television journalism have starred in negative ads—including two of the most searing ads of the Republican primary and the opening salvo by a Republican “super PAC” against President Obama.

Like superimposed newspaper headlines, network news footage is a staple of campaign advertising. But the extensive early use is new, and it may signal unprecedented usage to come as political advertisers seek the Holy Grail: support of the undecided voters on whom the election is expected to turn.

The campaign of former Gov. Mitt Romney, now the presumptive GOP nominee, dropped two network news bombs on his lead primary opponents. The first ad, except for the requisite disclaimer, was entirely comprised of then-“NBC Nightly News” anchor Tom Brokaw opening the January 21, 1997, broadcast by reporting that Speaker Newt Gingrich’s House colleagues had, “by an overwhelming vote,” found him guilty of ethics violations. (Disclosure: As nonpartisan analysts who track campaign advertising, we work for nearly every organization named in this article.)

Shown 2,225 times in the five days leading up to the Florida primary, the “Brokaw ad” will be one of the most remembered of the 2012 campaign. Onetime frontrunner Gingrich lost the state to Romney by 14 points.

On April 9, 15 days before the Pennsylvania primary on which former Sen. Rick Santorum was staking his campaign, a new Romney campaign ad opened with the voiceover by then-“CBS Evening News” anchor Katie Couric reporting Santorum’s loss of his Senate seat on election night in 2006. National political correspondent Gloria Borger (now at CNN) remarked that Santorum lost “among Democrats and independents, women and men, young and old, blacks and whites, rich and poor.”

The ad aired 177 times that day. Had Santorum stayed in the race, it probably would have aired through the state’s April 24 vote.

As of April 25, 284 spots had been aired by 64 advertisers in the 2012 presidential race. Of that group, these two ads strike us as the most effective and potentially trend-setting. Video is far more impactful than superimposed newspaper headlines that viewers have to speed-read. And even in a contest where all the voters are of the same party, credible voices like Brokaw’s and Couric’s may break through where unfamiliar narrators who are paid to sound shocked, shocked! won’t. Their words—and they themselves—become the most influential endorsers the candidates could ever command.

We are not among those who bemoan negative advertising—so long as it is accurate, as the Romney commercials were. But these ads also strike us as among the most worrisome of this cycle, at least from the perspective of broadcast journalism.

Newspapers, through their editorial boards, have a long tradition of endorsing candidates for office and regard the practice as part of their mandate to inform. Network news divisions, on the other hand, decided from the beginning of their comparably younger lives to go all-in on objectivity, even employing standards-keepers to help them avoid any appearance of bias because of the impact such an appearance could have on their credibility.

For the advertisers, the tactic of using objectively reported news footage is low-risk, high-reward. For the networks, the stakes are enormous: the professional investments of the involved news personnel, and untold millions of dollars in brand-building.

Networks are loathe to see their top journalists and news programming used this way, but have little recourse. When they protest, advertisers claim “fair use,” a tenet of US copyright law allowing limited use of copyrighted material without the owner’s permission. Television stations are especially leery of appearing to try to censor candidates by pulling their ads. (Networks and stations have somewhat better odds challenging the ads of super PACs and other outside groups, as CJR has previously noted.)

Elizabeth Wilner and Ken Goldstein collaborated on this article for CJR. Wilner is vice president of Kantar Media’s Campaign Media Analysis Group and former political director of NBC News. Goldstein is president of Kantar Media’s CMAG and a consultant to ABC News.