The invitation to the gala fundraiser for San Diego-based KPBS, one of 354 local stations in the PBS network, read "black tie or Downton attire".

Paula Kerger, president and chief executive of PBS, was attending with a friend. "She asked what I was going to wear and I said, 'No one's going to come in Downton attire, I'm going in black tie'. And we showed up, and we were the only ones in black tie."

Thanks to DVD and online catch-up viewing, social media chatter and the phenomenon of viewing parties – complete with upstairs-downstairs fancy dress – Downton Abbey has become the highest-rated drama ever to air on PBS.

Its success has helped generate goodwill towards PBS at a time when its funding sources have either been squeezed or threatened with obliteration. During last year's US presidential election, Republican candidate Mitt Romney said he would abolish the public PBS subsidy.

It was "the most serious threat to PBS in memory", Kerger told a public lecture organised by the RTÉ Audience Council in Dublin on Monday evening.

Federal funding
"I believe PBS and RTÉ have a lot in common," she said. But while it shares some market challenges, there are some rather large differences in how the two organisations are funded.

Speaking earlier that day in the RTÉ boardroom, Kerger outlines how the majority of PBS funding comes from philanthropy – donations , including funds raised from events such as the Downton-themed gala, outstrip federal funding and sponsorship.

“We get about 15 per cent of our funding from the federal government, not 50 per cent,” she says. But this is an aggregate figure across the network. For some PBS stations operating in smaller markets, the proportion of federal funding is closer to 50 per cent.

“I spend a lot of time trying to make people understand that if public funding was eliminated, it is the local stations around the country that will be impacted and some of them will go off the air,” says Kerger.

“I look at your system often and think, wow, that would be great.”

In the US, it was commercial television that came first, with not-for-profit broadcasting only arriving in the 1950s. Initially, it took the shape of unconnected stations producing “instructional television”, often from university campuses, and later it became the “co-op” that is now PBS, with stations sharing programming such as imported British dramas. Public television continues to play a much smaller role in the US than it does in Europe.

“We were very much from the beginning viewed as the kind of service that could fill in market failure, and that’s what we still are,” Kerger says. “We’re looking at what everyone else is doing and trying to figure out what’s not being covered.”

As US cable and commercial networks are not exactly failing in the drama department, PBS is not an active drama producer, preferring to acquire from the BBC and ITV. The "gaps" that it fills lie in arts and culture, science and history.

"There was the History Channel, but the History Channel isn't doing very much history any more. They're doing Swamp People."

Although it's "not a place you would come for breaking news", PBS adds "context" and "perspective" through its nightly News Hour programme, while it is making "a deep investment" in investigative journalism and exploring partnerships with other news organisations. News audiences are relatively smaller in the US, and Kerger marvels at the "extraordinary" viewing shares garnered by RTÉ's bulletins.

Competitive market
Downton's popularity notwithstanding, the best-known PBS programme remains the curriculum-based kids' classic Sesame Street, which has aired on public television in the US since 1969. (Romney, when attacking PBS, made sure to qualify that he "loved" Big Bird.)

Since Kerger was appointed head of PBS in 2006, she has made it one of her priorities to reinvigorate PBS’s educational kids’ output for the age of multi-platform consumption. “We had lost our sense of purpose,” she says. PBS now broadcasts five of the top 10 children’s shows in the US, in an increasingly competitive market.

"We're not accused of being unfairly advantaged, but what's happening is that people are copying what we are doing," she says. Competitors such as Disney have deep pockets. "It means that we have to be even more conscious of what it is we do that's different."