Ratings-challenged CNN hit rock bottom with primetime viewers in the most coveted demographic by advertisers — dealing a gut punch to embattled new boss Mark Thompson.

The cable channel, which touts itself as “the most trusted name in news,” drew just 83,000 viewers aged 25 to 54 during the week of May 13-19 from 8 to 11 p.m. — its lowest-rated week since 1991, according to Nielsen.

The three-hour block during the week features the network’s highest paid anchor, Anderson’s Cooper, with his show “AC360” at 8 p.m., along with “The Source with Kaitlan Collins” at 9 p.m. and “CNN NewsNight” with Abby Phillip at 10 p.m.

By contrast, Fox News garnered more than the twice the audience in the key demo, with 186,000 viewers, according to Nielsen. Left-leaning MSNBC was a distant second with 111,000, the data showed.

CNN’s total viewership for the week was also paltry with 494,000, compared with 2 million for Fox News — which shares common ownership with News Corp, the publisher of The Post. MSNBC pulled in 1.1 million, according to Nielsen.

Thompson, who was hired last August after the disastrous 13-month tenure of Chris Licht, has been under the gun to turn around the sagging ratings and modernize the organization.

Last month, Thompson said the network faces an “existential crisis,” as it deals with cord cutting and the shrinking cable TV business.

“There are plenty of things we have to fix at CNN,” Thompson, the former New York Times and BBC executive, said at the time.

He has left the struggling primetime lineup in place, while revamping the equally problematic morning schedule.

A spokesperson for CNN told The Post the network’s primetime ratings are “all growing year-over year” among viewers aged 25-54.

The rep added that the network’s primetime lineup, starting from “Erin Burnett Outfront” at 7 p.m. to its rebroadcast of “Anderson Cooper 360” at midnight, is “registering double-digit, year-over-year growth” in total viewers.

Thompson’s lack of bold moves since taking the helm last October has led to much consternation among staffers.

He unfurled a five-point plan on March 1 that included vague bullet-point items: “Building our digital future,” “A global integrated multimedia news operation,” “Future-proofing TV production,” “Developing new sources of revenue” and “Communication and culture.”

It was immediately panned by industry experts.

“It’s a five-point plan to make five-point plans,” a media exec told The Post at the time.

“In other words, there is no plan, but we are really planning to make lots of plans. And rest assured, there are lots of people overseeing the planning to make plans. And Mark is overseeing all of the people planning to make plans. So don’t worry. We’ve got this totally under control!”

Last week, Thompson publicly laid out a plan centered on CNN’s verticals, which has been described by insiders as a revision of the plan launched by former CNN boss Jeff Zucker seven years ago, in which the network launched culture- and lifestyle-focused digital verticals and tiered subscription offerings built around network personalities.

“We don’t believe news is just politics,” Thompson said during the company’s presentation to advertisers in New York.

“Business and tech are news. Climate and weather are news. Health, wellness, and living longer are news. So expect to see us build new branded verticals in all these areas on TV, on our apps, and across our other platforms.” 

One media insider said: “I know it’s cliché to say but Thompson is rearranging the deck chairs on The Titanic. He has no new ideas yet. But maybe his old media playbook will work. “

Thompson has made some internal leadership changes, including promoting Virginia Moseley — a hard-charging news executive who some staffers have called an “a–hole” and a “tyrant” — to lead the newsroom as executive editor.

He also canceled “CNN This Morning,” which had been co-anchored by Phil Mattingly and CNN veteran Poppy Harlow, who departed the network after being offered a lower-ranking job.

The ill-fated morning show was the brainchild of Licht, who was ousted shortly after the network cut ties with controversial anchor Don Lemon.