Kirstjen Nielsen defended the administration's practice of separating children from parents, but the president is said to have soured on her.
While the government has stopped large-scale separation of families, thousands of immigrants continue to arrive at the southwest border each month.
As immigration policies were developed under Donald Trump, Health and Human Services workers red-flagged "any policy which would result in family separation due to concerns we had about the best interests of the child," the Senate Judiciary Committee is told.
At least 50 under the age of 5 will be released with their parents by the Tuesday deadline imposed by a court, a government attorney says. However, that's only about half of the 100 or so children covered by the court order.
A judge in California gives border authorities 30 days to reunite immigrant families, and 14 days for those with children younger than 5.
The Trump administration issues a reunification fact sheet, saying it knows the location of all the children it has separated from parents or guardians at the border.
"... It's very strongly the Democrats' fault," the president says, rejecting criticism that his administration's "zero-tolerance" policy has resulted in inhumane and immoral conditions.
More than 1,600 people, including parents who have been separated from their children, are being transferred to federal prisons, U.S. immigration authorities confirm.