A little noticed event earlier this week brought ominous tidings to the Trump 2016 campaign, which spent most of the summer riding high on a wave of triumphalism and defiance against the GOP establishment machine. Donald Trump held a campaign event in Iowa, and CNN didn’t even acknowledge that it was happening. Indeed, while the assembled crowd waited to hear the latest Trump Brand Pablum in person, even CNN’s chryon blared on about the huge crowds that were at that moment being drawn by … Bernie Sanders.

This seems like such a small and insignificant thing – but only to those who have not been following the extent to which the cable networks have given Trump virtually unadulterated free coverage in exchange for the ratings boost that even mentioning Trump brought. As we noted here before, during a two week period in September, CNN spent 78% of its primary coverage time on Trump. As someone who watches cable news as a necessary incident of my job, I can tell you that the cable networks during that time period would have broken into coverage of literally anything they were otherwise talking about to report that Trump had just broken wind.

Trump’s phenomenon has always been mostly about a feeling – a sense that his supporters are part of a raucus party that is storming the gates and demanding attention from all comers. Two things are like oxygen to the Trump campaign – the media’s obsession with everything Trump does and says, and attacks from the other Republican candidates on Trump’s personality. His followers feed on this and revel in the way that everyone has to respond to everything Trump does, and take joy in how agog the rest of the candidates are of his bombast.

The feeling, though, has definitely changed, even if the poll numbers are lagging behind a bit. Trump no longer dominates social media mentions as a matter of course, and even when he acts out with one of his trademark stunts, he is barely capable of moving the needle. As the NY Times reported yesterday:

When Donald J. Trump responded in July to criticism from one of his Republican rivals, [mc_name name=’Sen. Lindsey Graham (R-SC)’ chamber=’senate’ mcid=’G000359′ ], by publicly releasing the South Carolina lawmaker’s cellphone number, the public and the press could not get enough of the jaw-dropping stunt.

But on Monday, when Mr. Trump sent a case of Trump brand bottled water to [mc_name name=’Sen. Marco Rubio (R-FL)’ chamber=’senate’ mcid=’R000595′ ]’s campaign office — poking fun at the Florida senator’s sweaty debate performance and penchant for chugging water — the prank fell notably flat.

While the cellphone gag earned 34,000 mentions in print, broadcast and social media that day, the Rubio water bottle gambit generated just 7,500 mentions — about one-fifth as many — during the same period, according toZignal Labs, a San Francisco-based analytics company that tracks media.

“A good old Trump stunt just doesn’t generate the media attention that it used to, even on social media,” said Anthony York, an analyst at Zignal Labs.

Though the New York real estate developer still leads the Republican field in national polls, Mr. Trump’s ability to command voter and news media attention simply by being his outlandish, bombastic self is starting to wane. The decline in attention for Mr. Trump seems particularly pronounced in the conservative news media that carry influence over many Republican primary voters.

Covering the Trump campaign has become a word that I never though I would use to describe it – tiresome. Even if you agreed with almost nothing Trump said or did, for a while there, he was a great muse for writing. Nowadays, picking up the keyboard to write another piece about Trump and what he’s said or done feels more like a chore than an exciting challenge.

Inertia will likely keep Trump at the top of the polls until there’s another major event that throws another candidate in the spotlight – perhaps the CNBC debate in a couple weeks. But the writing is on the wall for Trump’s lead, and when the end comes, it will come fast.

No campaign can long survive without its oxygen and Trump’s is currently gasping for air. It’s not hard to see that the end is near.