McALLEN, TEXAS — Nevada Sen. Catherine Cortez Masto this week joined a growing list of mostly Democratic lawmakers who are visiting the U.S.-Mexico border in search of answers about the status of thousands of migrant children who have been separated from their families — but left with few.

When she arrived here Monday, Cortez Masto was turned away from a holding center that is suspected to be housing dozens of separated children.

An employee of Casa Presidente, which also holds hundreds of unaccompanied minors who crossed the border, exited the sliding glass doors of what looks like a nondescript one-story office park, to tell the senator that she was not allowed in and that he couldn’t answer any questions. But he gave her a folded piece of paper of with a phone number, which the senator expected to be of little help.

“Red flags go up everywhere,” Cortez Masto said after being turned away. “That they’re trying to hide something or something is happening that they don’t want the public to know. And I think that, to me, is of more concern than anything I’ve seen so far.”

The lack of transparency on behalf of the administration and the Department of Homeland Security has only made the scenario more frustrating for lawmakers, for attorneys providing legal counsel and for the people caught up in the system.

That is why lawmakers, mostly Democrats, have traveled to the border in large numbers over the past three weeks to see for themselves the impact of President Donald Trump’s “zero tolerance” policy that has left more than 2,000 migrant children separated from their parents.

NBC News spent the day with Cortez Masto as she traced the path of parents who have been caught by U.S. Customs and Border Patrol and whose children were taken from them. While she wasn’t allowed in to talk with the children, she did enter a detention facility, which she likened to a prison, holding parents as well as the processing center where the separation occurred. NBC News was not allowed in any of the facilities.

It was a similar story, Cortez Masto, said for the six mothers and three fathers ICE officials let her speak to and the stories they shared about their own and their peers’ experiences.

She said the mothers all cried for themselves, for each other, as they told their stories. The senator relayed her conversation with a women named Ana who said she was fleeing for her life from Central America, but when she got to the U.S. to turn herself in for asylum, she was arrested and her five year old daughter was taken from her. Thirteen days later and she still doesn’t know where her daughter is.

All of the parents are worried they will be deported without their children.

She called the situation “devastating” and “heartless.”

The Nevada Democrat said she heard the same story through out the day: That these women and men fled a life of abuse or fears of violence. She came away hopeful, saying it is possible for the government to reunite all of the children with their parents despite the chaos that has ensued. But, she added, it depends on the government’s will.

“Do I think it can happen? Yes. Do I think this administration wants to? No,” Cortez said. “This administration very easily can focus on putting resources into a unit that just focuses on family reunification. They’re all coming through, they’re all identified.”

Cortez Masto said every parent and child is given an “alien identification” number. While the numbers don’t coordinate with their parents, Cortez Masto said that every person should be in the system.

Port Isabel ICE Detention Center in Los Fresnos, Texas holds adult immigrants, including parents separated from their children, who are awaiting deportation or court proceedings. Leigh Ann Caldwell

But part of the problem, she says, is that the parents are given no information and are asked no questions about who their children are to help identify them. And when parents call an 800 number for the Office of Refugee and Resettlement, no one answers.

Cortez Masto also saw the ugly side of the emotional immigration issue, too when when she came across the case of a four-month old baby brought across the border with a man who was not his father — something the man had already been caught doing once before.

That was at the processing center on Usula Avenue just three miles form the Hidalgo entry point and one of nine Customs and Border Patrol centers in the Rio Grande Valley. The building with a 20 foot high meshed chain-linked fence surrounded the property is also here where parents were encouraged to plead guilty and where their children were taken. Parents told Cortez Masto they and told, “either you are going to put your children on the bus or we’re going to do it for you,”

Meanwhile, back in Washington, Cortez Masto is working with a bipartisan duo of senators — California Democrat Dianne Feinstein and Texas Republican Ted Cruz — on a bill to prohibit the separation of children. But like any legislation pertaining to immigration in the past 30 years, Congress remains paralyzed on the issue so far.