John Sanders
© J. Scott Applewhite, AP
John Sanders, left, has resigned as acting commissioner of the Customs and Border Protection agency, effective July 5
The head of the Customs and Border Protection agency is leaving, and his replacement probably won't warm the hearts of advocates for immigrants.

John Sanders, the acting CBP commissioner, resigned Tuesday amid reports of migrant children at the border being held in unsafe and filthy conditions.

His resignation comes as public furor has increased over the treatment of detained migrant kids after lawyers reported some of the older children were caring for toddlers at a facility in Clint, Texas, and they lacked adequate food, water and sanitation.

Sanders is expected to be replaced by Mark Morgan, a former Marine and FBI agent who has been leading Immigration and Customs Enforcement (ICE) for fewer than two months, according to a senior administration official who spoke on condition of anonymity because the decision has not been finalized.

Morgan served as chief of the Border Patrol in the final months of the Obama administration, but he has since become a vocal supporter of President Donald Trump's hard-line immigration-enforcement strategy.

He defended the president's controversial decision to declare a national emergency to get funding to expand the southern border wall. "The president had no choice," Morgan said during a February interview on CNN.

When announcing Morgan's appointment to head ICE on May 5, Trump called him "a true believer and American Patriot."

And just last week, Morgan vowed to enforce Trump's plan, which has since been delayed, to ramp up arrests and deportations of families that have entered the country and had their asylum requests denied.

"If you come here with a child, that's a passport in the United States," Morgan said on the PBS NewsHour. "Nothing happens to you. That's a slippery slope, and no integrity in the system, and the rule of law is being eroded if we don't apply consequences."

Carla Provost, the head of U.S. Border Patrol, a component of CBP, was touring the border in Yuma, Arizona, on Tuesday when she learned of Sanders' resignation. The incoming head of CBP will be Provost's third boss since she took over the agency and its 19,500 agents in April of 2017.

Provost said the turnover at the top of CBP, and a broader leadership shakeup at the Department of Homeland Security, has not affected the work of Border Patrol agents as they deal with the ongoing surge of migrants crossing the southern border.

"I don't see that as having an impact on our ability to do our jobs and fulfill our mission," she said. "We have had support no matter what when it comes to the mission, when it comes to the crisis at hand in relation to the leadership."