MEXICO CITY — The father and daughter lie face down in the muddy water along the banks of the Rio Grande, her tiny head tucked inside his T-shirt, an arm draped over his neck.
The portrait of desperation was captured on Monday by the journalist Julia Le Duc, in the hours after Óscar Alberto Martínez Ramírez died with his 23-month-old daughter, Valeria, as they tried to cross from Mexico to the United States.
The image represents a poignant distillation of the perilous journey migrants face on their passage north to the United States, and the tragic consequences that often go unseen in the loud and caustic debate over border policy.
It recalled other powerful and sometimes disturbing photos that have galvanized public attention to the horrors of war and the acute suffering of individual refugees and migrants — personal stories that are often obscured by larger events.
Like the iconic photo of a bleeding Syrian child pulled from the rubble in Aleppo after an airstrike or the 1993 shot of a starving toddler and a nearby vulture in Sudan, the image of a single father and his young child washed up on the Rio Grande’s shore had the potential to prick the public conscience.
As the photo ricocheted around social media on Tuesday, Democrats in the House were moving toward approval of an emergency $4.5 billion humanitarian aid bill to address the plight of migrants at the border.
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Representative Joaquin Castro, Democrat of Texas and the chairman of the Hispanic Caucus, grew visibly emotional as he discussed the photograph in Washington. He said he hoped that it would make a difference among lawmakers and the broader American public.
“It’s very hard to see that photograph,” Mr. Castro said. “It’s our version of the Syrian photograph — of the 3-year-old boy on the beach, dead. That’s what it is.’’
The young family from El Salvador — Mr. Martínez, 25, Valeria and her mother, Tania Vanessa Ávalos — arrived last weekend in the border city of Matamoros, Mexico, hoping to apply for asylum in the United States.
But the international bridge was closed until Monday, officials told them, and as they walked along the banks of the river, the water appeared manageable.
The family set off together around mid-afternoon on Sunday. Mr. Martínez swam with Valeria on his back, tucked under his shirt. Ms. Ávalos followed behind, on the back of a family friend, she told government officials.
But as Mr. Martínez approached the opposite bank, carrying Valeria, Ms. Ávalos could see he was tiring in the rough water. She decided to swim back to the Mexican bank.
Back on the Mexico side, she turned and saw her husband and daughter, close to the American bank, sink into the river and get swept away.
On Monday, their bodies were recovered by Mexican authorities a few hundred yards from where they were swept downstream, fixed in the same haunting embrace.
“It is very unfortunate that this happens,” President Andrés Manuel López Obrador of Mexico said at a news conference on Tuesday. But as more migrants were being turned away by the United States, he said, “there are people who lose their lives in the desert or crossing the Rio Grande.”
Recent weeks have brought home the dangers along the border, though none quite as graphically as the death of Mr. Martínez and Valeria.
On Sunday, two babies, a child and woman were found dead in the Rio Grande Valley, overcome by the searing heat. A toddler from India was found dead in Arizona earlier this month.
And three children and an adult from Honduras perished when their raft overturned two months ago while crossing the Rio Grande.
Deterrence has been a favored strategy among American officials seeking to stem the tide of migration, even before President Trump took office.
In 2014, President Barack Obama pressed Mexico to do more after tens of thousands of unaccompanied children turned up along the southern border searching for loved ones in the United States.
Detentions in Mexico soared under the so-called Southern Border Plan.
But Mr. Trump, from the outset of his election campaign, has made a crackdown on illegal immigration a centerpiece of his presidency.
His administration has attempted to criminalize those entering the United States illegally, separated parents from their children and drastically slowed down the ability of migrants to apply for asylum in the United States.
More recently, his administration has imposed a plan to send thousands of asylum seekers back to Mexico to await their court proceedings.
Under sustained pressure from Mr. Trump, Mexico has been stepping up its own migration enforcement in recent months.
This effort accelerated in the past two weeks as part of a deal that the López Obrador administration struck with Washington to thwart potentially crippling tariffs.
As of Monday, the Mexican government had deployed more than 20,000 security forces to the southern and northern borders to try to impede the passage of undocumented migrants toward the United States, officials said.
But human rights experts, immigrants’ advocates and security analysts warned that the mobilization could drive migrants to resort to more dangerous routes in their effort to reach the United States.
For all the hard-line policies, hundreds of thousands of migrants continue to embark on the dangerous journey to the United States from Central America and elsewhere.
But for every migrant who chooses to take the journey, whether on foot, packed into cargo trucks or on the top of trains, the fear of what lies behind outweighs that which lies ahead.
Some are fleeing gangs that cripple the region and kill wantonly. Others are seeking an economic lifeline.
Such was the case with Mr. Martínez and his wife, who left El Salvador in early April intent on starting fresh in the United States, according to Jorge Beltran, a reporter for El Diario de Hoy in El Salvador who interviewed some of the couple’s relatives.
“They went for the American dream,” Wendy Joanna Martínez de Romero, said from her home in El Salvador.
Mr. Martínez quit his job at Papa John’s, where he had earned about $350 a month. By then, his wife had already left her job as a cashier at a Chinese restaurant to take care of their daughter.
The couple lived with Mr. Martínez’s mother in the community of Altavista, a massive housing complex of tiny concrete houses east of San Salvador, according to Mr. Beltran.
Though Altavista is under the control of gangs, the couple was not fleeing from violence, Rosa Ramírez, Mr. Martínez’s mother, told him. Rather, the grind of surviving as a family on $10 a day had become unmanageable.
Indeed, members of the family issued a plea to the public on Tuesday, seeking money to help repatriate the bodies of Mr. Martínez and Valeria. The cost was expected to be about $8,000 — an unimaginable sum for the relatives to manage.
Hours later, the Salvadoran government agreed to cover the costs.