PBS NewsHour,” once one of the nation’s most influential broadcasts, is on the brink of marginalization — if not extinction.

And for those of us who believe TV needs at least one noncommercial, nightly, national newscast in these increasingly corporate times, that’s a cause for concern.

The “NewsHour” has lost 48 percent of its audience in the past eight years, going from an average audience of 2.5 million viewers a night in 2005 to 1.3 million in fiscal year 2013 (PBS shows are measured in fiscal years).

That eight-year window was not chosen arbitrarily to find a headline-grabbing set of numbers.

With “NewsHour” in the news itself these days — after the first layoffs in its 38-year history and as partners Jim Lehrer and Robert MacNeil negotiate with WETA to have that Washington station take full ownership of the show — I went back to an interview I did with Lehrer in 2005 to try to remind myself what it was that I once liked so much about the newscast.

What instead seized my attention was the size of the audience as reported in that interview — and the huge loss since.

Of course, everyone in broadcast news has been losing big chunks of audience the last decade. But not like this.

The decline for “ABC World News” the past eight years has been 16 percent, while “NBC Nightly News” has lost 17 percent of its audience. “CBS Evening News,” meanwhile, is down 22 percent. That’s an average of 18 percent for the three commercial nightly news shows.

Furthermore, while the networks are talking average audience — the average number of people watching at any given minute — PBS is quoting cumulative figures — how many viewers the show “reaches” in live-plus-seven-days viewing.

By the more widely accepted standard, “NewsHour” is now under a million viewers a night, drawing an average audience of 949,000 viewers a night, according to Nielsen figures provided by a spokeswoman for the show last week.

But that’s only the tip of the iceberg when it comes to how far “PBS NewsHour” has fallen from the days of MacNeil and Lehrer, when it was considered essential nightly viewing for millions.

In Baltimore during the recently concluded October sweeps, the average nightly audience for “NewsHour” was 5,505 viewers overall, with 1,827 in the prime news demographic of 25 to 54 years of age, according to Maryland Public Television, which carries the show.

By comparison, “NBC Nightly News with Brian Williams,” which runs opposite the last 30 minutes of the one-hour PBS show drew an average audience in Baltimore in October of 104,000 viewers, with 29,000 of them in the prime demographic. That’s 19 times larger in overall audience.

If “NBC Nightly News” defines a national newscast, what do you call “NewsHour”?

And that’s not limited to Baltimore.

MinnPost, self-defined as “a nonprofit, nonpartisan enterprise whose mission is to provide high-quality journalism for news-intense people who care about Minnesota,” drilled down last week on the “NewsHour” audience there.

It found an audience of “about 1,800 people” in the 25- to 54-year-old demographic watching “NewsHour,” which it characterized as “startling” after doing some additional math and discovering that it amounted to 0.1 of a ratings point.

For the record, local news on WBAL-TV, the Hearst-owned NBC affiliate in Baltimore, drew an audience of 76,000 viewers, with 26,000 in the key demographic, airing opposite the first 30 minutes of “NewsHour” from 6 p.m. to 6:30 p.m. weeknights in Baltimore during October. That’s an audience 13 times as large as that of “NewsHour.”

Nor are the “NewsHour” troubles limited to ratings and money these days.

After 14 years, Ray Suarez left the PBS newscast last month. He has since joined Al Jazeera America, where he will start Monday as anchor of the nightly prime-time show “Inside Story.”