There has been no money set aside to combat the men, women and children who are bound for the American border, many of them fleeing violence or corruption, nearly all seeking better lives. The troops are tasked with the same types of logistical, support and even clerical jobs that National Guard soldiers sent to the border earlier this year are already doing.

The military’s morale issue is almost as worrisome. The deployment orders last until Dec. 15, meaning the troops will be on the border over Thanksgiving. They will have little to do beyond providing logistical support, unless Mr. Trump declares martial law. The troops will not be enforcing United States immigration law — that would run afoul of the Posse Comitatus Act of 1878, unless a special exception is made.

“When you give a soldier a real mission, you have less of a morale problem, even if it’s Christmas or Thanksgiving,” said Representative Anthony G. Brown, Democrat of Maryland and a former Army helicopter pilot who served in the Iraq war. “But when you send a soldier on a dubious mission, with no military value, over Thanksgiving, it doesn’t help morale at all.”

The soldiers, by and large, shy away from talking about the political winds that sent them to the border.