WASHINGTON >> While hiking the Appalachian Trail the other day, I became part of a Republican campaign attack on President Barack Obama.

Save the Mark Sanford jokes; I was (really) chaperoning a church youth group. Only after returning did I learn that my prevacation reporting about second-quarter job growth on CNBC had led off a 30-second television ad assailing Obama’s economic record.

It was merely a three-second factual observation — “The worst job-adding quarter in two years” — and not especially elegant at that. Yet beginning July 11, it was shown 6,136 times over six days in battleground-state media markets from Denver to Tampa, Fla., according to Kantar Media’s Campaign Media Analysis Group.

More and more this election year, campaign ads include footage from television news programs, further blurring the fading lines separating modern journalism and politics. The trend bothers practitioners of journalism more than those in politics.

“I thought you were particularly photogenic that day,” chuckled Karl Rove, a founder of Crossroads GPS, the Republican group that produced the ad featuring my work.

But of course that was not the reason Crossroads used the CNBC footage. They wanted to borrow a bit of credibility from the same “mainstream media” that they choose at other moments to bash as biased.

“When people see political ads, they think someone’s lying to them,” said Mark McKinnon, an ad-maker who worked with Rove on both of George W. Bush’s winning presidential campaigns.

“We try really hard to get credible third-party messengers to deliver facts,” McKinnon explained. “A fact coming from you is much more believable than a fact coming from us.”

As flattering as that might sound to journalists, our own credibility is hardly setting industry records right now. Which is precisely why journalists worry about the additional baggage of becoming associated with campaign advocacy.

“I don’t like it,” said Tom Brokaw, for years the face of one of the three major broadcast networks as anchor of “NBC Nightly News.” “It’s so hard to stay in what I call the ‘umpire mode.”’

Mitt Romney did not help him with an ad during Florida’s Republican primary this year. Fighting to fend off Newt Gingrich, the Romney campaign broadcast an ad consisting solely of Brokaw’s “Nightly News” report on a 1997 House ethics vote against Gingrich, then House speaker.

Brokaw and NBC News worried that the ad “compromised” his role as a journalist and asked that it be stopped. As they expected, the request was ignored; by Kantar’s count, the ad ran 2,225 times before Romney’s Florida victory.

Once campaigns feared such complaints from prominent TV journalists — and the hassle of responding to the lawyers who spoke for them. Now ad-makers from both parties shrug them off, as the prevalence of the practice increases their confidence that “fair use” broadcasting regulations makes legal threats toothless.

“I understand why Tom was angry,” said Bill Carrick, a veteran Democratic news media consultant. But, he added, “that’s a lost battle.”

It has been lost for several reasons, including the erosion of trust in politicians and the explosion of political talk on cable television. The expanded supply of available material ricochets rapidly among partisans via Twitter, Facebook and other social media, simplifying the job of ad-makers working on tight campaign deadlines.

“It’s very easy” to build an attack ad around TV news footage,” Carrick said. “You can put it together in a half-hour.”

A campaign like this one, centered around economic conditions, only increases the incentives to use TV talking heads as shortcuts. Personal scandals are easier to exploit in 30 seconds than fiscal policy and international debt crises.

“Illustrating the problems facing the American economy is very difficult to do,” said Elizabeth Wilner, a former political director at NBC News who is now a vice president at Kantar and a columnist for Advertising Age. Using TV journalists “provides compelling, credible footage to back up the ads’ arguments.”

As the ad featuring Brokaw shows, the technique is more broadly useful than that. Romney’s campaign in recent days rolled out an ad featuring TV footage of David Brooks of The New York Times, Mark Halperin of Time magazine, and Bob Schieffer of CBS News discussing the negative tone of Obama’s campaign.

“This was done without our permission,” Schieffer complained on “Face the Nation,” the Sunday talk show he hosts, after the ad made its debut. “I’ll get some blowback, I’ll tell you that for sure.”

I am less concerned, perhaps because my Crossroads speaking part is so brief and noncontroversial. As a grade-school student in 1968, long before CNBC existed, I appeared in a campaign ad that today would trigger far greater blowback. It was an ad for Robert F. Kennedy, whose campaign my father, Richard Harwood, was then covering for The Washington Post.

The stakes are also much higher for the likes of Schieffer and Brokaw, since I am the TV news equivalent of a Miami Heat bench-warmer to their LeBron James and Dwyane Wade. The major broadcast networks invest heavily in their superstar anchors, who as a result are especially sensitive to anything that could threaten their reputations and appeal to viewers.

But they also know they had better get used to it.

“I’m afraid we are just caught now in this world,” said Brokaw, now semiretired, from his home in Montana. “All the gates are down, and it’s not comfortable.”