Central American migrant caravans
Mark Morgan told NPR the new rule virtually ending protections, which he called a "pilot," is not being applied to the whole border and likely will be blocked.
Beginning Tuesday, asylum seekers who pass through another country first will be ineligible for asylum at the U.S. southern border.
A San Diego TV station accessed leaked documents, revealing the operation.
The latest caravan began Monday night with many women and children boarding buses bound for the Guatemalan border.