Rosa Ramírez pleaded with her son, urging him not to leave El Salvador and head north with his wife and young daughter. The risks were simply too high.

He saw no other choice. Their neighbourhood was controlled by a gang that enriched itself through drug-dealing, extortion and violence.

But most pressing of all, Ms Ramírez said, they could barely make ends meet on their jobs at fast-food restaurants, and had pinned their hopes on making it to the United States.

They never did.

Last Sunday, after weeks on the road, Ms Ramírez’s son, Óscar Alberto Martínez Ramírez, 25, and his 23-month-old daughter, Angie Valeria, drowned while trying to cross from Mexico into Texas.

Their fate, captured in a searing photograph of father and daughter lying face down in the muddy waters of the Rio Grande, her arm limply wrapped around him, has quickly become a focal point in the debate over the stream of migrants pushing towards the US border – and President Donald Trump’s determination to stop it.

Critics of the president have taken up the case of the Martínez family, with Senator Chuck Schumer of New York calling the president’s policies “a whirlwind of incompetence, leading to pictures like this”.

Mr Trump and his supporters, in turn, have accused Democrats of an inaction that has worsened the crisis, with Senator Mitch McConnell of Kentucky criticising them as being “uncooperative and uninterested in anything except political posturing”.

But for many residents here in Mr Martínez’s hometown, San Martín, the heated political battle in Washington has barely registered, and President Trump’s repeated efforts to block migrants have had little impact on the decision to make the perilous journey.

“He can say what he wants — that he’s going to put up a wall of I-don’t-know-how-many metres,” said José Alemán, 48, a partner in a local car washing business. “But they keep going.”

The death of Mr Martínez and his daughter has given an urgent and poignant face to a major driver of migration from Central America and elsewhere: economic duress.

Much attention in recent years has been given to the rampant violence that has compelled so many Salvadorans and residents of neighbouring Guatemala and Honduras to head north.

But perhaps a bigger impetus, officials and residents here say, has been economics, especially poverty and the lack of good jobs.

The Martínez family made it as far as the northern Mexican border city of Matamoros last weekend, where, according to relatives, they hoped to cross into the United States and apply for asylum.

Told the bridge was closed, however, they decided to ford the Rio Grande on Sunday afternoon instead.

Mr Martínez went ahead with the couple’s daughter, carrying her on his back, tucked under his T-shirt. His wife, Tania Vanessa Ávalos, followed behind, riding on the back of a family friend, she told Mexican officials.

As Mr Martínez, carrying their daughter, approached the opposite bank, he was visibly tiring in the rough water, Ms Ávalos told the authorities. Unnerved, she decided to swim back to the Mexican side, but she saw her husband and daughter, close to the American riverbank, sink into the water and get swept away.

“I didn’t want them to go,” Ms Ramírez, Martínez’s mother, said this week in an interview at the small, two-bedroom row house she had shared with her son and his family. “But they didn’t take my advice.”

It remains unclear how the Martínez family intended to argue their case for asylum, or whether they even understood the legal basis for gaining such protection. Ms Ávalos did not respond to requests for an interview.

But Mr Ramírez repeatedly said her son and his family were not fleeing persecution or the threat of it — requirements for gaining asylum in the United States.

Donald Trump laughs at Florida rally as supporter suggests shooting immigrants

They migrated “only because of the economic situation”, she said. “Lamentably, the salaries here are very little and they aren’t enough,” she added, speaking softly.

Mr Trump has railed against what he calls rampant asylum fraud, and he has imposed restrictions on the system in an effort to curb abuse — measures that human rights and migrants’ advocates say have imperilled the lives of asylum-seekers who have legitimate claims.

Residents and officials here say a gang dominates the neighbourhood, Altavista.

But Ms Ramírez and another relative said the immediate family had not been directly imperilled by the gang.

Instead, like so many others here and throughout the working class of El Salvador, the family was struggling to get by, living on the edge of poverty.

“There isn’t opportunity, there’s no work,” said Víctor Manuel Rivera, the mayor of San Martín. He estimated that about 50 per cent of the municipality’s residents with a high school degree are unemployed.

“Every day I hear it: ‘I’m leaving for the United States’,” he said.

People here talk about “la situación” — the situation — shorthand for the economic struggle many face. The counterpoint is often simple: “the American dream”.

“It hasn’t occurred to me to leave for there,” said Salvador Humberto Andrade Torres, 59, a neighbour of the Martínez family, referring to the United States. “But it occurs to a lot of people.”

Officials described the neighbourhood — indeed, the entire municipality of San Martín — as a de facto “bedroom community”, with many residents commuting on average about two hours each way to work in the capital, San Salvador.

Mr Martínez and Ms Ávalos, however, worked relatively close to their home, family members said — she in a Chinese fast-food restaurant at a middle-class mall, and he at various branches of the Papa John’s pizza chain.

But the couple, even though they were sharing household expenses with Ms Ramírez and her partner, were having a hard time on their salaries of about $300 (£236) a month.

Last autumn, they started talking about migrating to the United States.

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Most of those who migrate are young, as has been the case for generations.

But in recent years, the municipality has seen a sharp increase in the number of families migrating, too, part of a wave of family migration from Central America towards the United States.

Ms Ramírez said she spoke with her son from time to time as the family made its northward trek, but he did not reveal many details.

“I would ask him and he said, ‘We’re fine, we’re fine,’” she recalled.

The farewell had been subdued. The family gathered for a simple, Sunday meal one afternoon last spring. Ms Ramírez prepared beef stew — “they love that”, she said.

Several days later, as she headed to her night shift at the garment factory where she works, Ms Ramírez said one last goodbye to her son and his family.

When she returned in the morning, they were gone.

Ms Ramírez remembered her son as a loyal, doting father and “a responsible, friendly, respectful son”.

Her granddaughter, Angie Valeria, Ms Ramírez recalled, was “happy, intelligent”.

As she spoke, she sat on a worn sofa covered in a sheet decorated with the images of princesses from animated Disney films. A single bare light bulb illuminated the room, a few ceramic butterflies adorned the walls.

After the bodies were discovered on Monday, Ms Ramírez found herself scrolling through the photos of her son and granddaughter on her phone. Her daughter eventually erased them to spare her the pain.

“I would feel bad when I looked at them,” Ms Ramírez said.

It is an agony that she hopes others will never have to suffer.

“Don’t risk the lives of your children,” she said, hoping to warn others against setting off on the potentially dangerous journey to the American border. “Those who are thinking about this, don’t do it.”

“I’d prefer to live here, in poverty, than risk my life,” she added. “But we don’t all think the same way.”