They comprise the majority of the border force, and have focused both on installing concertina and other barriers to slow down any rush of migrants, and building temporary camps in which USA soldiers can live nearby.
Asylum-seekers are encouraged to go to ports of entry to ask for help, but are often forced to wait weeks or months to do so because the USA government admits only a limited number at a time for processing.
As the Daily Wire reported, pushback against the caravan has escalated in Tijuana, with hundreds of Tijuana residents gathering on Sunday to protest the unmanageable influx of migrants.
"Out! Out!" they chanted, demanding that the caravan be diverted and anxious about the impact of many hundreds of migrants and asylum seekers stuck in their city for months.
"Asylum seekers are registering their names in a tattered notebook managed by migrants themselves that had more than 3,000 names even before the first members of the leading caravan started arriving last week", Fox reports.
Some Tijuana residents supported the migrants, but others accused them of being messy, ungrateful and a danger to the city. They also complained about how the caravan forced its way into Mexico, calling it an "invasion". And they voiced worries that their taxes might be spent to care for the group.
"We don't want them in Tijuana", protesters shouted.
"The problem is that there has been bad information circulating on social media, with videos of two or three migrants acting badly, climbing the wall or grabbing food in stores", said Coronel, adding that most are poor people simply trying to find work.More news: US envoy hopes for peace deal with Taliban in 2019, says media
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And in Mexico City, authorities closed a shelter at a sports complex that had once housed thousands of migrants. The remaining 650 migrants from the third, mainly Salvadoran, caravan were taken to a Roman Catholic pilgrimage hostel at the Basilica of Guadalupe.
"The Haitians arrived with their papers, with a clear vision", Gastelum said in an interview posted on the city's Facebook page.
Last month, thousands of Central American migrants began a long journey from Honduras through Mexico toward the United States to seek asylum.
"They're coming here with an American dream that doesn't exist", said Aranguer.
Donald Trump tweeted about Mexico's inability to deal with the many migrants staying and passing through the country. On Nov. 14, Mattis told a soldier who asked that question that the mission so far was to install the barriers, and "we'll let you know" what the ultimate plan is. "How can they think we are going to come here to be violent?"
Another migrant caravan of around 150 people reportedly set off from El Salvador for the U.S. on Sunday.
Edwin Alexander Gomez, 20, told AP in San Salvador that he wants to work construction in NY, where he hears the wages are better and the city is safer.
The U.S. military continues to patrol and secure the border amid escalating tensions with the arrival of thousands of Central American migrant in Tijuana.