For weeks before the midterm elections, President Trump warned ominously about the threat from a caravan of migrants streaming from Central America toward Mexico’s border with the United States. It was a fearsome mix of criminals and “unknown Middle Easterners,” Mr. Trump claimed darkly, one that constituted a genuine national emergency.
But since the election last week, Mr. Trump has tweeted about the caravan exactly once — to issue a proclamation preventing those who cross the border illegally from applying for asylum in the United States. Fox News, which faithfully amplified Mr. Trump’s warnings about the migrants, has gone similarly quiet on the subject.
There was little dispute, even before Election Day, that Mr. Trump was exploiting the caravan for political purposes. But analysts, historians and veterans of previous administrations said there were few comparable instances of a commander in chief warning about what he called a looming threat, only to drop it as soon as people voted.
While the caravan has faded from television screens, the costs of Mr. Trump’s response to it have not. Nearly 6,000 active-duty troops remain deployed from the Gulf Coast to Southern California, where they are putting up tents and stringing concertina wire to face a ragtag band that is still not near the border.
“Now that the political utility of troops on the southern border to face a fictitious caravan invasion threat is over,” said Adm. James G. Stavridis, a former commander of the military’s Southern Command, “let’s hope the president will stand down the troops so they can be with their families — especially over the holidays.”
But some officials in the Defense Department worry that Mr. Trump could do the opposite — seek an exception to the Posse Comitatus Act, the 1878 law that prohibits the government from using active-duty troops to enforce laws inside the country’s borders.
.. voters who made up their minds in the last three days before the election said they voted for Democrats over Republicans 53 percent to 41 percent. That coincides with the period in which Mr. Trump redoubled his focus on the caravan, rejecting the advice of aides who wanted to air a commercial promoting the healthy economy.
.. At one campaign rally after another, Mr. Trump said the election came down to “the caravan, law and order, and common sense.” In Mesa, Ariz., on Oct. 19, he said: “You got some bad people in those groups. You got some tough people in those groups. And I’ll tell you what — this country doesn’t want them. O.K.? We don’t want them.”
.. A day earlier, he tweeted about the “assault on our country at our Southern Border, including the Criminal elements and DRUGS pouring in.”
Mr. Trump posted footage of an undocumented immigrant on trial for killing a police officer, and his campaign organization produced an ad featuring migrants trying to scale a wall to dramatize the stakes of the election.
“I’ve never before seen an American president, after going all over the country about this national crisis, then the day after an election shrug,” said Douglas Brinkley, a presidential historian at Rice University.
The closest parallel that Mr. Brinkley drew was to President Lyndon B. Johnson, who seized on — and mischaracterized — two murky encounters between American and North Vietnamese warships in the Gulf of Tonkin in 1964 as a pretext to accelerate America’s engagement in the Vietnam War. Still, he said, Mr. Trump’s response was of a different order.
“It was a dangerous form of xenophobia, aimed solely for electoral purposes and had nothing to do in the end with real national security,” Mr. Brinkley said.
For the troops, so far, it has mostly been an expensive field trip. The cost of the deployment is not known, but budget officials believe it could reach $200 million if all 15,000 troops that Mr. Trump pledged are ultimately sent.
.. Defenders of Mr. Trump said the troops would take little notice of his sudden lack of emphasis on the caravan.
“Knowing the troops, knowing how busy they are, they’re not focused on him,” said Jack Keane, a retired four-star general who is a former vice chief of staff of the Army. “They’ve got a job to do.”
But other former military officers said the soldiers were well aware of the political motivation behind their mission. Lacking much else to do, they will quickly pick up on Mr. Trump’s loss of interest in the caravan, and it will add to their already depleted morale.