A sweeping new ICE operation shows how Trump's focus on immigration is reshaping federal law enforcement

In mid-May, White House deputy chief of staff Stephen Miller, frustrated over what he saw as numbers of arrests and deportations of unauthorized immigrants that were too low, berated and threatened to fire senior Immigration and Customs Enforcement officials if they did not begin detaining 3,000 migrants a day, according to two sources who spoke to attendees.

WASHINGTON — In mid-May, White House deputy chief of staff Stephen Miller, frustrated over what he saw as numbers of arrests and deportations of unauthorized immigrants that were too low, berated and threatened to fire senior Immigration and Customs Enforcement officials if they did not begin detaining 3,000 migrants a day, according to two sources who spoke to attendees.

Miller also threatened to fire leaders of field offices posting the bottom 10% of arrest numbers monthly, the two sources said.

Weeks later, ICE is launching the Trump administration’s largest immigration crackdown.

“Operation At Large,” a nationwide, ICE-led plan already underway to ramp up arrests of unauthorized immigrants, includes more than 5,000 personnel from across federal law enforcement agencies and up to 21,000 National Guard troops, according to an operation plan described to NBC News by three sources with knowledge of the personnel allocations who detailed the previously unreported plans.

Drawing those numbers from other law enforcement agencies, though, has been a source of tension among some officials, who feel they have been taken off other core national security missions, according to three additional law enforcement and military officials. Like others interviewed for this article, they requested anonymity in order to share sensitive information.