For broadcast networks, the evening news broadcast is a cherished part of their legacies — having brought the likes of Walter Cronkite, Tom Brokaw and Peter Jennings into living rooms over the decades.

But with pressures mounting on the traditional TV business, the American institution is in a period of flux.

The traditional TV audience is a slow melting glacier, with network evening newscasts down nearly 1 million viewers in the 2024-25 season compared to the previous year, according to Nielsen. As a result, network news executives will be on edge this year, with two of the three broadcasts undergoing major overhauls.

Next month, NBC will replace longtime “Nightly News” anchor Lester Holt with Tom Llamas, 45, who helms the streaming NBC News Now program “Top Story.” It will mark only the fourth change in the “Nightly” role since 1983.

This comes after “CBS Evening News” in January replaced Norah O’Donnell with a duo of John Dickerson and Maurice DuBois. Conceived by outgoing “60 Minutes” executive producer Bill Owens, the new “CBS Evening News” has aimed to do longer segments instead of the headline-driven style the broadcasts are known for.

Although broadcast networks have largely ceded scripted TV shows to streaming, they are still protective of the news programs. Both NBC and CBS are trying to improve their competitive position against “ABC World News With David Muir,” which has its largest lead over the second-place peacock network in 30 years.

Like other TV newscasts, evening programs are in a battle to maintain relevance amid competition from not only cable and streaming but also YouTube, which attracts older audiences as well as younger, digital-savvy viewers.

“No one wants a tombstone that reads ‘Here lies the guy who killed the evening news,’” said Jonathan Wald, a veteran producer who worked with Brokaw on “NBC Nightly News.”

Evening newscasts on ABC, CBS and NBC — all of which launched in the late 1940s — are among the few shows that still drive appointment viewing.

They’ve held up better than most TV network genres. Nielsen data show the programs are watched by an average of 18 million viewers a night and reach 71 million each month despite competition from 24-hour cable news and a barrage of digital platforms.

Many weeks throughout the year, Muir’s broadcast is the most watched program on TV, often averaging 8 million viewers.

So far, the audience isn’t buying the changes on “CBS Evening News.” The program has dropped below 4 million viewers in some weeks since its launch and occasionally gets topped by “Special Report With Bret Baier” on Fox News.

NBC News executives believe Llamas can provide a fresh spark for “Nightly News.” They’re encouraged that he led in the 25-to-54 age group on recent nights when he filled in for Holt.

“We think he’s exactly the right guy at this moment,” said Janelle Rodriguez, executive vice president of programming for NBC News. “He is someone who has worked at this literally since he was a kid.”

But there is always risk involved when an anchor change occurs — programs typically see a shift of 500,000 viewers in the aftermath. A single audience share point decline in the Nielsen ratings can mean about $10 million less in ad revenue.

Evening news broadcasts are still profitable businesses and have benefited from increased advertiser demand for audiences watching live TV. In 2024, ad spending on the three network evening newscasts, including the weekend editions, hit $669 million, according to measurement firm iSpot.tv, an increase of 12% over the previous year.

The programs also still provide an identity for ABC, CBS and NBC. A recent study by research firm Magid found that 50% of consumers cite news as their top reason for watching a network TV affiliate.

Most people tuning in at 6:30 p.m. to watch are older viewers who likely grew up with the habit, as evidenced by the commercial breaks. The data from iSpot show around 46% of the ad dollars spent on the programs are for pharmaceutical products.

Competitors have long taken shots at “World News,” calling it a shallow broadcast that delivers a lot of stories without much detail. ABC News executives counter that Muir has traveled around the world to do lengthier reports that are expanded into documentaries for Hulu.

“We spend a lot of time making sure the show is informative visually and reflects a modern, elegant broadcast,” said Chris Dinan, Muir’s executive producer. “David knows television. He’s a student of it.”

Viewers, who like Muir and the visual sizzle of “World News,” have made it No. 1 for nine consecutive years. “You can’t listen to the chattering classes,” said Wald.

For most of his tenure, Muir has maintained a neutral image that protected him from right-wing claims of bias made against many mainstream journalists.

That changed last fall as Muir and colleague Linsey Davis became targets after they vigorously fact-checked President Donald Trump at the second presidential debate in September. “I’m not fans of those guys anymore,” Trump said during a Fox News appearance. “And his hair was better five years ago.”

Trump’s anger at Muir has had no impact on the ratings for “World News,” which have remained steady.