U.S. Sen. Jeff Merkley (D-Oregon) visited a detention center for immigrant children near the Mexico border Sunday in an attempt to draw attention to the Trump administration policy of separating children from parents.

Parents, even those credibly seeking asylum, have been separated from their children as part of the White House policy.

At least 600 children were separated from their parents last month.

The detention center in Brownsville, Tex. is run by the nonprofit Southwest Key Program at a location called Casa Padre, which was a former Walmart turned detention center, according to Merkley.

No member of Congress has visited the facility, says Merkley, who in the past two years has become one of the most vocal critics of Trump administration policies, sparking speculation that he will run for president in 2020.

After his team failed to get permission for him to tour the facility, he went to the front doors anyway.

Merkley, accompanied by multiple video cameras and the American Civil Liberties Union, shot a Facebook live video as he attempted to gain access to the facility.  (The video had been viewed more than 353,000 times within the first several hours.)

He was initially told that a manager would come speak to him when he telephoned into the facility from the front door. The police arrived first.

The nonprofit Southwest Key Program has been a longtime contractor for the U.S. government to house minors who crossed the border unaccompanied, but Merkley called on the nonprofit to reconsider its work housing minors taken from their parents after entering the United States.

"Americans should be outraged by the fact that our taxpayer dollars are being used to inflict spiteful and traumatizing policies on innocent children," he said in a statement.

The nonprofit's website directs inquiries to U.S. Health and Human Services' Administration for Children and Families. An email to the agency was not immediately returned Sunday evening.