Acting Customs and Border Protection (CBP) commissioner John Sanders is resigning from his role as the top immigration enforcement official amid renewed scrutiny over the treatment of young migrants in U.S. custody at detention centers. CBP sources tell CBS News his resignation will be effective July 5.

Sanders was installed at CBP after its former chief, Kevin McAleenan, was tapped to fill the top spot at the Department of Homeland Security after former Secretary Kirstjen Nielsen stepped down. President Trump told reporters on Tuesday that he did not ask Sanders to resign, but noted he "knew" a change at the agency's top was coming.

According to a senior administration official, Mark Morgan, Mr. Trump's previous choice to lead the U.S. Immigration and Customs Enforcement (ICE), will now be tapped to take over the acting role at CBP. Morgan, a Border Patrol chief under the Obama administration, has publicly backed the the president's border wall plans.

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Sanders' departure from the administration comes after public outrage over reports of hundreds of migrant children who were found last week living in squalid conditions at a border protection facility in Texas. Roughly 300 of the children at the Clint, Texas facility, just outside El Paso, were moved to other sites after reports emerged about the conditions, but about 100 have since been returned to the facility, a CBP official told CBS News on Tuesday.

The concerning conditions follow a pattern of similar issues that materialized in the wake of the administration's "zero tolerance" policy which resulted in the separation of thousands of migrant children from their parents instituted last year.

In an interview with Hill TV on Monday, President Trump argued that conditions at those facilities are "much better than they were under President Obama."

"When I came in, I took over Obama's policy. It was a policy of separation. I'm the one that put them together," he said. While that's partly true, what developed into the Trump administration's approach was modeled after Operation Streamline, a program started by the Bush administration in 2005. That program referred all illegal immigrants for prosecution, but made exceptions for adults traveling with children.

The Obama administration then used that model as well, but detained families together in ICE custody. Mr. Trump eventually passed an executive order ending family separations last June, but the government has admitted it could take years to identify the thousands of children separated from their parents.

In an Oval Office ceremony Tuesday, the president said he was "very concerned" about conditions at migrant detainee facilities but criticized Democrats for, in his view, blocking a border supplemental bill even as House leaders work to get a bill passed.

On Capitol Hill, Democrats lambasted the president's constant revolving door at the top immigration post amid news of Sanders' leave.

House Homeland Security Committee Chairman Rep. Bennie Thompson said in a statement that the resignation "adds fuel to the chaos at the Department of Homeland Security."

The Democrat added, "CBP is clearly failing to carry out its mission given the Trump Administration's disastrous immigration policies. It is quite clear that bad actors in the White House are doing all they can to strong-arm the Department of Homeland Security and stand in the way of any progress or agreeable solution."

Speaking on the House floor on Tuesday, Democratic Rep. Jim McGovern of Massachusetts said Sanders had succumbed to "public pressure," but "unfortunately, the president keeps replacing with people who continue to enforce policies that are cruel ... that separate children from parents at the border ... and treat children worse than animals at the border."

Sanders joined CBP in July 2018. He was previously an adviser for an investment firm and CEO of a private intelligence firm.

Emily Tillett contributed to this report.