Marchers protest the Trump administration's policy of separating children from their parents as families arrive at the nation's southern border. (Alfredo Corchado/Dallas Morning News) (The Dallas Morning News / By Alfredo Corchado)

"There are many in this crowd whose families, whose own story is the same ... Jimenez, Martinez, or O'Rourke. This one is Kennedy," he said, referring to his own family's Irish roots. "That story is our story.... This is the story of our country, the nation that we have built. No president, no administration is going to take that away from us."

The protesters marched along fields. Some pushed baby strollers and others carried children in their arms, in the backdrop of pecan orchards just yards from the white tents that are holding the minors at the Marcelino Serna Port of Entry, named after a Mexican immigrant who joined the Army in 1917 to avoid deportation. He went on to become the most decorated Texas soldier in World War I.

Tornillo is about a 40-minute drive from El Paso, where temperatures have lately hovered around 100 degrees. Authorities say the tents where the minors are being held are air-conditioned.

About 200 children are in custody there now, but with the capacity for thousands, many more could arrive in the days and weeks ahead, O'Rourke said.

"We would like to think, and we try to tell ourselves, this is not America, this is not us, this is not what we do," he said. "But ladies and gentleman, at this moment, this is America, this is us, this is what we are doing."

Marchers protest the Trump administration's policy of separating children from their parents as families arrive at the nation's southern border. (Alfredo Corchado/Dallas Morning News) (The Dallas Morning News / By Alfredo Corchado)

O'Rourke is challenging Republican Sen. Ted Cruz in this November's midterm elections.

Cruz, who defends the Trump administration's policy, says the treatment of unauthorized immigrants is similar to how other lawbreakers are handled.

"As a U.S. citizen, if you commit a crime and get arrested, you're separated from your kids," he said. "And if you're the only caregiver, your children have to find alternative caregivers — whether family members, friends or foster care. What all the media attention on separation of families is really saying, is don't incarcerate those who come here illegally."

West Texas has become the epicenter of the country's controversy over immigration in recent weeks as the region has seen a dramatic rise in enforcement actions, including deploying National Guard troops, extending the border fence, now referred to as a "wall," and separating families.

The zero-tolerance policy is aimed at deterring families from crossing the border without permission, but advocates for immigrants say factors such as gang violence and remnants of U.S.-led conflicts that have pushed families to flee Central America will not go away soon.

Attorney General Jeff Sessions quoted the Bible last week to defend Trump's hard-line stance, arguing that God ordains the laws of governments to ensure order.

But critics, including some Republicans, say the policy is creating chaos, leaving some families without information about where there children are or when, and if, they'll be able to find them.

Sessions' remarks have drawn criticism from religious leaders of different faiths.

"Bless us, Lord," said Father Tom Smith, director of Holy Cross Retreat Center in Las Cruces, N.M., who joined the protesters Sunday. "Help us to recognize that the Scripture is used to bring unity, compassion and love, not to justify a law, which is unjust, or to justify those want to oppress."

Eliot Shaplieh, a longtime El Paso political leader, said the policies against illegal immigration are contrary to the spirit of the United States.

U.S. Rep. Joe Kennedy, D-Mass., joined protesters near Tornillo, Texas to protest Trump's immigration policies. Next to him is U.S. Rep. Beto O'Rourke, raising his arm. (Alfredo Corchado/Dallas Morning News) (The Dallas Morning News / Alfredo Corchado)

"In the America of El Paso and the border, and across Texas, we should welcome those who have made our country great, our communities great," he said. "They are among the hardest-working immigrants ever to come to our country."

Gabriel Vasquez, 33, a Las Cruces City Council member, had planned to watch Mexico play Germany in Sunday's World Cup match until he saw O'Rourke's invitation via Twitter.

"If we don't come, who else will defend us?" he said, adding that he was heartened by the response, with lines of vehicles surrounding the area. "We have to defend our rights. I see this is as our obligation."