The Pentagon’s border mission had previously been scheduled to end Dec. 15, and the Defense Department later extended the deployment into January. Then came Monday’s announcement.

In a rare use of military force first announced in October, the Trump administration sent about 5,900 active-duty troops to join with Border Patrol agents and National Guard members, as a caravan of Central American migrants made its way toward the United States.

The move was viewed by many as unnecessary political fear-mongering as the midterm elections approached. Border and military officials insisted the caravan was a serious threat.

On Monday, the Pentagon said its “assistance” would continue through Sept. 30 at the Department of Homeland Security’s request, and the support would focus on “mobile surveillance and detection” and placing concertina wire “between ports of entry.”

It’s not clear exactly how many troops are at the border or how the number is expected to change — a Pentagon official said in November that the number was expected to dip below the 5,900 initially deployed. The Pentagon did not immediately answer further questions about Monday’s announcement.

The extension comes as a new migrant caravan was forming in Honduras, and President Donald Trump and Congress’ differing visions on border security have led to the longest shutdown of the federal government in U.S. history.

Trump continues to push for a wall to stem what he calls a crisis at the border.

But the reality is more complicated.

Illegal border crossings have declined for nearly two decades, and border-crossing apprehensions in 2017 were at their lowest level in more than 45 years.

But a record number of families have tried to cross the border in recent months, and asylum claims have jumped as many migrant families say they fear returning to their home countries.

The troops, who are prevented by the Posse Comitatus Act from engaging in law enforcement activities within the country, had been spread across small bases where they spent the initial weeks setting up concertina wire and other security barriers. Later, the troops were also giving rides to Border Patrol agents and conducting more training.

This article originally appeared in The New York Times.