"What are you waiting for, Obama?" shout the social media, the tweets and disaster videos that have been the world's window into Syria for two years.
"What more evidence do you need?" ask the rebels and their activist supporters, pummelled daily by Assad's rockets and jets.
Even the White House admits that to those instruments of war have, in all probability, been added chemical weapons; these were US President Barack Obama's avowed "red line", whose use would finally trigger intervention of American might in the Syrian horror.
So has the time finally come when America and its allies will take action, send in the bombers, declare a no-fly zone? It seems not.
For there is a matching shout from the West: "It's Iraq all over again."
Indeed, if there are any polls suggesting intervention would be a vote-winner, governments across the world are keeping quiet about them. The Syrian people bleed, world leaders tear their heartstrings, but their voters, tired of war, tired of recession, tired of politics, just want to turn the other way.
On Thursday, the Obama administration performed a U-turn as remarkable as any we are likely to see in the carefully modulated world of international relations. For days, its operatives poured doubt on reports that the use of chemical weapons in Syria had been confirmed.
First Britain, then Israel, claimed to have "credible evidence" that Assad's regime had used nerve agents such as the instantly lethal sarin on opponents.
Caveats, as always, applied, but tests on samples taken to Porton Down, the British Ministry of Defence's science lab, were put alongside dramatic videos, in which young men and women were wheeled into hospitals, foaming at the mouth, their eyes glazed, irises expanded to the point where pupils almost disappear.
But Chuck Hagel, the US Defence Secretary, who was on a tour of the Middle East that included Israel, had this to say on Wednesday: "Suspicions are one thing, evidence is another." He said that US intelligence agencies were "still not convinced".
Less than a day later, the White House had changed its mind. "Our intelligence community does assess, with varying degrees of confidence, that the Syrian regime has used chemical weapons on a small scale in Syria, specifically the chemical agent sarin," it said in a letter to senators.
It turned out the Pentagon had been running its own tests – on different samples from the British – and had come to the same conclusion.
"A decision to come to that conclusion" had been taken within the last 24 hours, Mr Hagel said on Thursday, covering himself neatly but perhaps unconvincingly.
There was clearly politics afoot here. The US was caught short by the sudden pronouncements from its two closest military allies. The difference in position, at a time when the West is trying to put a united front on its Syria policy, was deeply embarrassing.
The British put out a simultaneous statement on Thursday, which was less noticed as its headline component confirmed what the Foreign Secretary, William Hague, had pretty much already said about "credible evidence".
The main purpose of the release, as far as co-ordination with Washington was concerned, came further down: "The information we have is persuasive but not sufficient to identify the perpetrator."
Once again, Washington and London are on the same page: Assad did it, but we don't have the heavy burden of proof required to do anything about it. That is a neat fix that spares the blushes of Mr Obama, who was elected on a ticket of withdrawing troops from the Middle East and whose reluctance to involve them in a new front is palpable.
But it will hardly satisfy the beleaguered Syrian population, many of whom want Mr Obama to come to their rescue.
We have been here before; in Iraq, yes, but not necessarily Iraq 2003. In 1989, a great conference of the western powers was held in Paris, to assess the evidence that Saddam Hussein had used chemical weapons in his war with Iran and, egregiously, on Iraqi Kurds whom he regarded as an enemy within.
It was presented with concrete evidence, down to chips of paint from shell casings, that chemical weapons had been used; that the same weapons had been deployed repeatedly during the course of the war; and that the targets were in every case enemies of the Iraqi state – the Kurds, or the Iranians.
Even then, the conference refused to name and shame Iraq as the perpetrator. It is hard to expect the international community to be more decisive now.
Most chemical weapons experts agree with the Western position, that the highest standards of proof have not been met. One objection raised can be dispensed with – many observers have pointed out that the numbers killed are small relative to the 5,000 Kurds killed in Saddam Hussein's attack on Kurdish Halabja in 1988, and officials have speculated that "diluted" forms may have been used.
Amy Smithson, an expert at the James Martin Centre for Nonproliferation Studies in Washington, gives a simpler explanation: chemical weapons degrade when not kept properly. Saddam Hussein had to renew his every six months. They could just be using small quantities of degraded gas.
On the other hand, she agrees there are other plausible explanations – they could have come from industrial or other chemical stores (less likely, if sarin); they could have been obtained by rebels and deployed to push the US into action; the symptoms in the videos – the frothing at the mouth – could be the result of any number of reagents; most importantly, she says, weapons inspectors like to have control over "the chain of custody" – to take and transfer the samples themselves, rather than relying on intermediaries, with the possibility of contamination.
"The White House letter and Secretary Hagel both state concerns with chain of custody," she said.
"Serious indications of sarin use, yes; bullet-proof case, no."
So maybe the politicians are right. For all the misery, it is too soon to intervene. But for those forced to watch as Syria disintegrates, it is painful to stand aside. A diplomatic analyst, Shashank Joshi of the Royal United Services Institute, says President Assad could be playing the same game as Iran with its nuclear programme – testing the West's "red lines" as a ploy to sow confusion.
He says, though, it remains "puzzling" what Assad hopes to gain by risking Western intervention. Indeed, if it forces America to take leadership of the West's response to the crisis, the regime may have signed its death warrant. One thing this debate has done is to show how much our response to the conflict is being dictated by our experiences of previous wars.
Politicians have been determined to avoid repeating the errors of the Iraq invasion of 2003, but also of watching as another Middle East dictator uses weapons of mass destruction on his own people.
The irony is that their policies run the risk of driving us to repeat all of them together. Chemical weapons or no, it is surely time for a change of tack. (© Daily Telegraph, London)