WASHINGTON (AP) — The White House on Thursday withdrew the nomination of a longtime border official to lead U.S. Immigration and Customs Enforcement as the Trump administration grapples with a massive increase in Southern border crossings that are straining the system with no easy solution, according to people with knowledge of the move.

The paperwork on Ron Vitiello was sent to members of Congress Thursday, the people said, and the decision was unexpected and met with confusion. Vitiello had been scheduled to travel with President Donald Trump to the border on Friday, but was no longer going, one official said. He will still remain acting director, they said.

ASSOCIATED PRESS Ron Vitiello, who has been acting director of U.S. Immigration and Customs Enforcement, was withdrawn on Thursday. The decision was unexpected and reportedly met with confusion.

One Homeland Security official insisted it was nothing but a paperwork error that had later been corrected. But other, higher-level officials said the move did not appear to be a mistake, even though they were not informed ahead of time.

The people had direct knowledge of the letter but were not authorized to speak publicly and spoke to The Associated Press on condition of anonymity.

Vitiello was nominated to lead ICE, the agency tasked with enforcing immigration law in the interior of the U.S., after more than 30 years in law enforcement, starting in 1985 with the U.S. Border Patrol. He was previously Border Patrol chief and deputy commissioner U.S. Customs and Border Protection, which oversees the patrol.

Vitiello took over during a time of unprecedented spotlight and scrutiny for the agency. Part of ICE’s mission is to arrest immigrants in the U.S. illegally, which has made it a symbol of President Donald Trump’s hardline immigration policies.

He had been acting head since June 2018, nominated in August, had a Senate confirmation hearing in November and his nomination had passed one Senate panel, the people said. But because Homeland Security touches on so many topics, a second committee also had jurisdiction and his nomination was still under discussion there. Some Democrats had concerns, and a union representing some ICE agents had opposed his nomination.

Department of Homeland Security officials referred questions to the White House, which did not respond to multiple requests for comment.

The move by the White House came as immigration officials were dealing with a 12-year high in U.S-Mexico border crossings — and a recent flare-up by Trump who once again threatened to close the border entirely by the end of this week, before backing off.

For many years, families arriving at the border were typically released from U.S. custody immediately and allowed to settle with family or friends in the U.S. while their immigration cases wound their way through the courts, a process that often takes years and has been derided by Trump as “catch and release.”

But in recent months, the number of families crossing into the U.S. has climbed to record highs, pushing the system to the breaking point. As a result, ICE was releasing families faster, in greater numbers and at points farther removed from the border. Since Dec. 21, the agency set free more than 125,000 people who came into the U.S. as families.

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Associated Press writer Jill Colvin contributed to this report.