Prior to the midterms, the president employed harsh anti-immigrant rhetoric to describe the “caravans” of migrants — many of them women and children — fleeing their homelands.

In an effort to fire up his nationalist base, he repeatedly called the caravan an “invasion” of the US, claiming without evidence that “Middle Easterners,” terrorists and hordes of violent gang members had infiltrated the group.

He ordered the troop deployment, and ominously warned that the active-duty troops would stop the asylum-seekers, though their actual role turned out to be building camps and stringing barbed wire along the border.

Trump barely mentioned the caravans after the midterms, and the Pentagon announced that the border operation, briefly dubbed “Operation Patriot Freedom” before the brass scrapped that moniker, would be wound down and that the troops would be home by Christmas.

Some of the migrants have massed at the border city of Tijuana, while others remain hundreds of miles away from the US.

Experts eyed the order warily.

Posse Comitatus is “always looming in the background. You never invoke it as such because it is such a background principle,” William Banks, author of “Soldiers on the Home Front: The Domestic Role of the American Military” and former director of the Institute for National Security and Counterterrorism at Syracuse University, told the website.

Kelly said in the directive that the move was necessary because “credible evidence and intelligence” suggest that the migrants in Tijuana “may prompt incidents of violence and disorder” that could threaten Border Patrol personnel.

But the White House could still find itself in legal hot water if the authorities in the memo are determined to be counter to the law, Banks said.