The real migrant bus king of North America isn't the Texas governor. It's Mexico's president.

PIEDRAS NEGRAS, Mexico – It took Ana Elizabeth Melgar four tries to reach the U.S. border.

Each time she made her way north, Mexican immigration authorities caught her and bused her south – not to her home country of El Salvador but to a city in southern Mexico .

"If you catch me and I am a migrant, send me back to my country," she said, while resting in a Catholic shelter in this Mexican border town across from Eagle Pass, Texas . "I get it: I don't belong here. But what is this nonsense that you're sending me south in Mexico? It's illogical."

The Biden administration and Texas are taking credit for an unusual springtime lull in illegal border crossings, with the White House touting its legal pathways and Gov. Greg Abbott championing his troops and concertina wire. But analysts, immigrant advocates and migrants themselves say it's Mexico blocking the path north.

Mexico President Andrés Manuel López Obrador's immigration agency has intensified a busing program that aims to hurt migrants' chances of reaching the U.S. border – or at least delay their arrival – by apprehending them on highways, train routes and airports and shipping them to the southernmost part of his country.

López Obrador is likely motivated by economic interests. Last fall, a surge of hundreds of thousands of migrants flooding the U.S. Southwest created a hurdle to trade between Mexico and the U.S., its largest trading partner by far.

Immigrant advocates say the policy drives vulnerable people into the arms of smugglers. Migrants report being extorted on routes north only to be intercepted at checkpoints and returned to southern Mexico to do it all again.

"The Mexican government is busing people in circles," said Andrew Selee, executive director of the Washington, D.C.-based Migration Policy Institute.

"The numbers aren't down because of busing in Texas," he said. "The numbers are down because of busing in Mexico."

U.S. Customs and Border Protection reported fewer than 189,372 migrant encounters in March, down slightly from 189,914 in February, during a time when migration typically starts to spike. Encounters were lower than normal through the first 10 days of April, too, according to congressional testimony .

The drop bucked historical, seasonal trends and was "only the second time this century that encounters declined from February to March," said Adam Isacson, director of defense oversight for the Washington Office on Latin America.

Mexico cracks down on migrants: 'more checkpoints, more buses'

The busing program is a response, analysts say, to the surge in migrants arriving from Venezuela and other countries where Mexico, like the U.S., can't easily return people. Mexico's foreign ministry, interior ministry and immigration agency, the Instituto Nacional de Migración, didn't respond to requests for comment.

Mexico's crackdown is evident in the number of migrant encounters resulting in a person being detained or placed in a shelter – but not deported.

These encounters ballooned to more than 726,000 in 2023, according to Mexico's interior ministry, from fewer than 179,000 in 2021. In January and February alone, Mexico reported more than 230,000 encounters with migrants who were placed in detention or shelters and then released.

Melgar was among them.

On a recent Tuesday in April, while migrants milled about the shelter or ate breakfast, she sat alone on a courtyard bench and smiled. After more than four months of trying, she had made it to the U.S. border.

While Melgar rested, the nun in charge, Sister Isabel Turcios, led a group of American women on a tour. Medical volunteers set up an outdoor clinic in the courtyard. There were 108 migrants sheltered that day – hardly any compared with last year, Turcios said.

In December, thousands had arrived daily in Piedras Negras and other points just south of the border. That month, on the U.S. side, U.S. Customs and Border Protection reported its highest-ever one-month tally of migrant encounters: 301,981.

That same month, presidents Biden and López Obrador had a phone call in which they discussed " additional enforcement actions ," and Biden dispatched a high-level team of negotiators to Mexico City.

By mid-April, the checkpoints had multiplied.

Mexican authorities had set up at least six immigration checkpoints between Monterrey and the border at Piedras Negras , according to Turcios' conversations with migrants. It had become onerous even for her, a nun from El Salvador, to travel overland.

"The authorities got together and decided: more checkpoints, more buses to take the migrants south," she said. "The numbers started to go down for that reason and because they were rounding them up.

Texas' numbers haven't been going down "because of the barbed wire," she said. The migrants who make it through Mexico's checkpoints "keep passing under the wire."

Texas border czar says 'tactical infrastructure' deters crossings

That same day, across the Rio Grande in Eagle Pass, Texas, the state's first "border czar" Mike Banks climbed up the sloped river bank to address his troops in Shelby Park, the city park that has become ground zero in the state's public battle with the Biden administration over border enforcement.

Banks shouldered past reams of concertina wire and got nicked on the way.

The three tiny cuts on his upper forearm were evidence, he said, of the difference between "concertina" wire that grabs the skin and "razor" wire that slices through it. It was a lesson in the "tactical infrastructure" that he says is deterring illegal border crossings in Texas.

"I will tell you that, right now, if it wasn't for what we are doing in the state of Texas, you wouldn't see our numbers the way they are," Banks told USA TODAY.

Texas is taking credit for the dip in migration along the state's 1,254-mile border with Mexico. Banks, a former Border Patrol agent, and his boss, Gov. Greg Abbott, say the state's $11 billion Operation Lone Star is working, and the numbers prove it.

Texas registered a sharper drop in migrant crossings in the first three months of the year than the border did as a whole, according to CBP statistics, while California saw crossings increase .

"This entire sector is averaging a couple of hundred (migrants) a day versus 4,000 to 6,000 just in this park" last year, Banks said, referring to Border Patrol's Del Rio Sector. "So the deterrence is working and, look, Texas is going to protect Texas."

Other Republican-led states are pitching in: 16 states have sent troops or law enforcement officers to support Operation Lone Star, according to a spokesman for the governor's office.

The state has also aimed to export the border crisis across the country : Abbott's Operation Lone Star has bused more than 112,700 migrants to Democrat-led cities nationwide.

In Texas, migrants are offered the bus rides and go voluntarily. In Mexico, authorities give them no choice.

During his recent visit to Eagle Pass, Banks, who advises the governor, addressed a circle of camouflage-clad agents of Florida's Fish and Wildlife Conservation Commission. He joked with a group of Texas highway patrolmen as they took a break from the heat in a shade tent where two stray dogs napped.

The river was quiet but for two Honduran men who had been at Turcios' shelter earlier that day. They waded along the U.S. bank looking for a spot to clamber up through the concertina wire.

'Cold, heat, hunger, thirst'

Melgar, a mother of three, worked as a seamstress in Costa Rica for years, making money she couldn't earn in El Salvador.

But she returned to her country when work dried up. In December, under pressure to pay for her now-teenage children's education, she left for Mexico with her sights set on the U.S.

Mexican immigration agents clad in brown uniforms first picked up Melgar in the colonial city of Puebla, in southern Mexico, she said.

The second time, they intercepted her in the northern factory town of Torreon.

The third time, they caught her in Monterrey, a wealthy business hub south of Texas.

Each time, she was bused back to a migrant detention center in southern Mexico, held for a few days and then released, she said.

On her fourth attempt, she skirted multiple Mexican checkpoints by riding atop a cargo train and walking for miles through arid desert. She spent "days and days and nights of cold, heat, hunger and thirst," she said.

Melgar said she applied for an appointment to cross the border lawfully, via the CBP One app, but she hasn't received one yet.

"I'm waiting," she said in a WhatsApp message last week, while still at the shelter. "God willing, it will come soon."

How long will Mexican enforcement last?

Mexico's immigration crackdowns rarely last as long as they have this time.

"The reality is that Mexico has made it harder for people to get to south Texas," said Aaron Reichlin-Melnick, policy director at the American Immigration Council. "It’s this broad shift as a result of Mexican enforcement – one we might see breaking down."

Already there are signs of a breakdown along the U.S.-Mexico border, nearly 500 miles northwest of the Eagle Pass-Piedras Negras crossing.

Migrants have been reaching Ciudad Juárez, across from El Paso, Texas, in larger numbers in recent days, and tension at this border crossing has grown.

The El Paso Border Patrol Sector has seen average daily migrant encounters tick up slightly from 940 earlier this month to 1,025 as of Friday.

Earlier this month, more than 140 migrants breached reams of concertina wire on the El Paso side of the Rio Grande and confronted Texas troops. A local grand jury indicted the migrants on misdemeanor riot participation charges, according to the district attorney.

Then, last week, a cargo train hailing from the outskirts of Mexico City rumbled into Ciudad Juárez with hundreds of men, women and children atop its boxcars. If the train stopped at the military and immigration checkpoint outside the city at all, the authorities let it go.

Adults held fast to the children or shaded them under blankets until the train slowed, and the migrants climbed down, blocks from the U.S. border, to decide their next move.

Contributing: Omar Ornelas, El Paso Times

Lauren Villagran can be reached at lvillagran@usatoday.com.

This article originally appeared on USA TODAY: The real migrant bus king of North America isn't the Texas governor. It's Mexico's president.