Julie Hirschfeld Davis, New York Times, April 3, 2018

President Trump said on Tuesday that he planned to order the military to guard parts of the southern border until he can build a wall and tighten immigration restrictions, proposing a remarkable escalation of his efforts to crack down on migrants entering the country illegally.

Mr. Trump, who has been stewing publicly for days about what he characterizes as lax immigration laws and the potential for an influx of Central American migrants to stream into the United States, said he was consulting with Jim Mattis, the secretary of defense, about resorting to military deployments.

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The active-duty military is generally barred by law from carrying out domestic law enforcement functions, such as apprehending people at the border. But previous presidents have deployed National Guard troops to act in support roles on the border with Mexico — former President Barack Obama sent 1,200 in 2010 and former President George W. Bush dispatched 6,000 in 2006. Governors of border states have done the same when faced with large inflows.

Mr. Trump has spoken before about launching a military operation to police the border, only to have his aides walk back the remarks amid a backlash from members of his administration and officials in Mexico.

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Mr. Trump’s comments on Tuesday came after he kicked off his third consecutive day of tweeting about America’s “weak” border laws and called on Congress to act on legislation to toughen immigration laws. The push comes as Mr. Trump has complained with increasing urgency about a large group of migrants from Honduras that has been traveling through Mexico.

The caravan has been a popular topic on Fox News — the president’s favorite news network — and his aides have argued that weak immigration policies are luring the migrants from Central America to the United States.

“The big Caravan of People from Honduras, now coming across Mexico and heading to our ‘Weak Laws’ Border, had better be stopped before it gets there,” he tweeted on Tuesday. “Cash cow NAFTA is in play, as is foreign aid to Honduras and the countries that allow this to happen. Congress MUST ACT NOW!

Mr. Trump’s Twitter tirade on immigration policy started Sunday with threats to and, since then, he has consistently threatened to pull out of the North American Free Trade Agreement, known as Nafta. On Tuesday, Mr. Trump said Nafta “is in play,” and repeated his contention that Nafta was a “cash cow” for other nations.

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Late Monday, Mexican immigration officials started to negotiate with the caravan’s organizers. And Mexican authorities have agreed to provide humanitarian visas to the migrants so that they can stay in Mexico legally, a representative from Pueblo Sin Fronteras said.

On Tuesday, Mr. Trump claimed credit for having persuaded Mexican officials to break up the caravan.