One of today’s great ironies is that the 24-hour news channels are usually at their worst when real news is breaking.

At best, the term “cable news” is a misnomer. Actual news coverage rarely exceeds 10% of a channel’s day. The rest of the time is devoted to opinions and arguments over current events. It takes a weak mind and strong stomach to view CNN or MSNBC for any length of time. Fox, of course, also has its limits.

But the inherent weakness of cable news was brought home — yet again — with Saturday’s coverage of the London terrorist attacks that left seven civilians dead and 48 wounded. The anchors knew something serious had happened, but they had no clue of its extent, let alone the motives behind the mayhem.

As a result, for hour after hour, TV screens were filled with stupefyingly boring video of parking emergency vehicles with lights flashing and of crowds milling aimlessly on the streets.

Meanwhile, the anchors, their voices dripping with concern, kept spewing the same meager set of facts over and over. Guest commentators, either on screen or on the phone, provided some backup, but they didn’t have any information to impart, either.

In short, the news crews were in an impossible situation. It’s like taking members of the Royal Shakespeare Company, throwing them onto the Second City stage and demanding they perform first-rate improv.

One way cable channels can avoid such embarrassments is by showing some discretion. Someone should have the guts to make the call when apparent terrorist attacks don’t deserve wall-to-wall coverage.

For openers, Saturday’s attacks didn’t happen in Boston, Detroit or Houston. There’s an ocean between America and London, so an atrocity there is no sign of terror activity here. Also to be considered  — at the risk of sounding callous — is the small number of casualties. Seven dead and 48 injured are a serious matter, but bus accidents in the U.S. that have had bigger tolls barely get mentioned on the national news.

For instance, the July 16, 2016, truck attack in Nice, France, was worthy of every moment of attention. Not only was the toll staggeringly high with 86 dead and 434 wounded, but it also was the debut of a new terrorist tactic. The truck smashing into crowds has been copied many times since.

It’s understandable why the channels stuck with their no-news coverage of London. Their audiences are not constant, so new viewers were always turning in to learn about ongoing developments.

But there should have been some breaks for real news while the crews waited for authorities to provide important information about the attacks.

Until that information was forthcoming, the channels would have served their audiences just as well if they had offered a screen saver with a news crawler at the bottom giving all the known facts. It would have saved everyone a lot of grief.

Health care. Russia. Travel ban. Wiretapping. Budget cuts. Leaks. And on and on and on.

Work up a lather, rinse, repeat.

O Lord, grant me relief from the endless cycle of “news” based on the possibly informed insights, half-truths, pure speculation and outright lies that pass as journalism these days.

Never has so much blather been spent on issues that are no more real than unicorn dust or three-legged Martians. Talk about Russia’s links to the 2016 election or illegal wiretapping is ridiculous until the probes are done. Fury or relief over health care changes is silly until the legislation gets through the sausage factory known as Congress. Same with the budget.

As for the travel ban, its outcome is uncertain until it finally gets out of the hands of judges who don’t understand executive authority and confuse campaign speeches with the wording of legal action.

You want solid information? You’re better off these days spending time on Pinterest projects or following some nobody’s Twitter account.

The problem is, outside of Donald Trump, news is impossible. It doesn’t happen anymore. He hasn’t just sucked up all the air in the room — he’s inhaled the Earth’s entire atmosphere. If anything that doesn’t involve the Prez is going on, it’s not getting a dab of ink, a digital pixel or a moment of airtime.

It’s all so boring.

When I was a young man, the idea of a 24-hour news channel seemed like a dream. Most people had only three options for national and global news — CBS, NBC and ABC — and they provided just 22 minutes a day. As a Detroit suburbanite, I could watch Canadian news, which offered a broader outlook on the world. I could only imagine what vistas a daylong news station would open up.

Ted Turner once considered news a joke. When the feds told him to add a news program to Atlanta’s WTBS to fulfill its public service requirements, he put a dog on the air alongside a human anchor. But after TBS became a hit on cable systems, Turner figured he could make more bucks with an all-news channel. Thus was born CNN.

From the start, CNN was a disappointment, offering repetitious reports on easy-to-cover news. Soon enough came the parade of talking heads to tell us what the news really meant. Gee willikers! Instead of being bored every Sunday morning with Meet the Press or Face the Nation, we got a chance to hear puffed-up pundits seven days a week.

My hopes rose briefly when MSNBC came along in 1996; at the time, thanks mainly to David Brinkley, NBC’s news operation was respectable. But MSNBC followed CNN’s template from the start and never distinguished itself until transmuting into a lunatic asylum for deranged leftists.

By the time Fox News came along, the mold for 24-hour news had become unbreakable. But at least we finally got news that the other channels ignored, plus some conservative viewpoints.

The basic problem is all three news channels are obsessed by immediacy instead of context. Got a wildfire in California, snowstorm in New York or school shooting in Colorado? Brace yourself for the wall-to-wall coverage. The networks are like a dog with a bone that keeps gnawing away long after the last shred of meat is gone.

Yes, at times, the networks have provided a tremendous service. CNN earned its stripes with its Gulf War reporting, and all three channels were invaluable on Sept. 11, 2001.

But the tendency to dwell on a single topic above all else is worse than ever today. CNN and MSNBC are hellbent on destroying Trump, and Fox is dedicated (sort of) to protecting him. The coverage has been going on nonstop since Nov. 9, and I’m done in by fatigue. Maybe you are, too.

But it has to end sometime, preferably soon. Because I have a tip for the news networks:  Trump ain’t going anywhere, so get used to him.