PRESIDENT TRUMP’S order deploying thousands of active-duty troops to the U.S.-Mexico border, to halt what he characterized as an imminent “invasion” by so-called caravans of Central American migrants, had its use as pre-electoral political theater. But it is not a laughing matter.

Taxpayers are already on the hook for a bill likely to exceed $200 million over the next several weeks to support at least 7,000 soldiers whose mission, insofar as the Pentagon has described it, is unlikely to involve detaining or deporting any of the Central Americans who make their way to the frontier. Rather, the U.S. service members are expected to provide support — helping spot incoming migrants; transporting Border Patrol agents by helicopter; stringing concertina wire on existing border barriers; providing emergency medical care if needed.

That’s a big if. Military planners estimate that just a fifth of the roughly 7,000 mainly Honduran migrants heading northward by foot through Mexico are likely to reach the border. And Pentagon officials have made clear that those who do make it that far are unlikely to pose a threat to national security. Journalists traveling with the migrants report that more than half of them are women and children, not the hardened criminals and Middle Easterners — “the worst scum in the world” was the president’s baseless characterization — that Mr. Trump conjured to inflame his Republican base before the midterm elections.

Presidents Barack Obama, George W. Bush and Bill Clinton all sent National Guard troops to the border but in generally much smaller numbers and on better-defined grounds; they, too, were criticized for shows of force whose security value was more symbolic than real. Mr. Trump’s choice to use active-duty troops, and in numbers wildly disproportionate to any conceivable threat, is posturing masquerading as policy.

Mindful perhaps of that problem, and the potential for mockery — troops confronted by women and children — the Pentagon on Wednesday redubbed the mission, which had been known as Operation Faithful Patriot, a handle brimming with phony drama and peril. From now on it will be known simply as “border support.”

Border Patrol agents detain hundreds of thousands of migrants at the Mexican border annually — a fraction of the number routinely apprehended 20 or 30 years ago. While the number of family units now crossing to seek asylum in this country has spiked, the overall cross-border flow remains modest compared with recent decades’ numbers.

It’s worth noting that migrants who present themselves at established border crossings to request asylum in the United States are breaking no law; they are entitled to do so under statute and international treaties. (They are also entitled to apply for asylum if they cross between border posts, illegally, though on Wednesday the administration announced it would try to change that — a change in long-standing practice that seems to fly in the face of U.S. law and international treaties.) That it serves Mr. Trump’s political purposes to use asylum seekers to fan fears does not make those migrants an actual danger.

The administration is entitled to urge migrants not to come, to stress that most are unlikely to be granted asylum, and to work with governments in Mexico and Central America to those ends. To brandish U.S.  troops under the current circumstances is unlikely to work as deterrence. Now that the elections are finished, maybe this pointless deployment can be ended.

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