At the hospital in Reyhanli, a small Turkish border town that took in many of the victims, the mourners gathered outside mostly came from just two extended families, Mr. Youssef’s and the Abu Amash family.
The families are connected by marriage and both come from Khan Sheikhoun, the village in rebel-held Idlib Province that residents said been hit with chemical weapons earlier that morning.
“Just look at this!” said Orwa Abu Amash, 33, as he held up his phone. On the screen was a long WhatsApp message listing what he claimed were the names of 46 relatives who had died that day in Khan Sheikhoun.
As Mr. Youssef paced around the parking lot outside the hospital, he said he was scared not just for his wife on the other side of the hospital wall, who had arrived lying motionless on a stretcher, but for his relatives on the other side of the border. Many of them had also been poisoned by the gas but had not been deemed sick enough to be treated in Turkey, whose border is closed to most Syrians.
Earlier Tuesday, witnesses reached by phone in Syria described similarly traumatic scenes at the site of the attack.
Warplanes had roared overhead just before 7 a.m., when many people in the town were sleeping after a night of intense sounds of bombing, said Othman al-Khan, an activist in Khan Sheikhoun who was reached via phone at a first aid station.
He spoke after fleeing Rahmeh Hospital in Khan Sheikhoun, where many victims were being treated, after an airstrike hit part of the hospital. While he was speaking, another loud boom sounded, and the line went dead; he called back to say it had been another nearby strike.
The rebel-held area’s minister of health, Mohamad Firas Al-Jundi, said in an online video that hospitals and clinics were overwhelmed. He said he had been in a field hospital at 7:30 a.m. when more than 100 people arrived injured or sickened; many others, he said, were sent to other clinics, with some left lying in the corridors.
Symptoms, he said, included suffocation, fluid in the lungs with foam coming from the mouth, unconsciousness, spasms and paralysis.
“It’s a shocking act,” he said. “The world knows and is aware of what’s happening in Syria, and we are ready to submit evidences to criminal laboratories to prove the use of these gases.”
Yasser Sarmani, a rebel fighter reached by phone in Idlib, said he collapsed while driving to the scene on his motorcycle to help the victims. “It became a routine for us that when we hear an airstrike to rush to the scene and try to rescue people,” he said. “I woke up to the sound of an explosion, but it was not as loud as usual.”
“Driving against the wind, my eyes started burning and I felt I was being suffocated,” he added. “People were running away from the site and falling on the ground. It was a cruel scene. At that point I fainted.”
He said he woke up an hour later at a clinic, after receiving injections and oxygen. “Kids were all over the floor, some dead and others struggling to breathe,” he said. “The noise of them trying to breath was loud, with foam all over their faces.”
As they watched the ambulances come and go outside the hospital in Reyhanli, Mr. Youssef and several of his relatives wondered what President Trump might make of all this.
On Monday, Mr. Trump’s administration signaled that it no longer saw the departure of President Bashar al-Assad of Syria as a priority. On Tuesday, Mr. Assad appeared to unleash one of the worst chemical attacks of the war.
“If Donald Trump is happy for this to happen to his own people and his own children,” said Mr. Youssef, “then we’re happy to keep Bashar al-Assad.”
Shuffling around in the hospital parking lot, several of Mr. Youssef’s relatives buried themselves in their phones, watching the videos of the morning’s atrocities over and over.
The clips have been widely circulated on the internet. They show the pale corpses of dead toddlers, or the retching bodies of men who appear to be close to death.
One gray-haired woman lay on her back, her purple leggings exposed. A young boy, perhaps 12, lay motionless except for his mouth, gasping for air. None had visible marks of injury. Some of the sickened and dying were nearly naked, as rescuers, many with their bare hands, stripped them and hosed them down.
A man narrating a video of motionless children, lined up as if sleeping, was able to come up only with sentence fragments. “A whole family,” he repeated.
Unlike the people around the globe who found these videos on social media, several of those watching them outside the hospital in Reyhanli had witnessed the scenes in real life.
You wouldn’t have known it, however, by looking at their blank faces. “We’ve seen so much of this,” Mr. Abu Amash said. “It’s normal. We see this every day. We had six years of it.”
