But, in typical unorthodox fashion, he took to Twitter on Saturday to call off the operation, praising Mexico for its work in stemming the tide of US-bound migrants.
Trump also took aim at Democrats, urging them to cooperate on his proposed reform of US asylum policy. Otherwise, he said, the planned deportations would go ahead after all in two weeks' time.
The land border crossing between the Mexican city of Tijuana and the US city of San Diego is the busiest in the Western Hemisphere. And, on the Mexican side, many are deeply concerned that Trump's threat to deport millions of people would precipitate a humanitarian crisis.
Tijuana is already overwhelmed by the thousands of migrants from Central America waiting for their asylum applications to be processed.
Overcrowded emergency shelters"The situation along the border is chaotic, not just because of Trump's threats, but also because of Mexico's government," Valeria Griego of Tijuana's Casa del Migrante told DW. The institute provides emergency accommodation for migrants is the oldest such institute in the city. It was founded by the Congregation of the Missionaries of St. Charles Scalabrinians over 30 years ago. At the moment, the shelter is completely overcrowded. Griego said she had no idea how the Mexican government plans to deal with the situation.
"We have space for 150 people," Griego said. "We reached our maximum capacity weeks ago, and now we only take in women and families, as well as men traveling with young children." The city's other migrant shelters, of which there are roughly 20, find themselves in a similarly critical situation.
Read more: In Mexico, migrants must choose between bad and worse
A gargantuan logistical challengeAbigail Andrews, a sociologist at the University of California in San Diego, told DW that it was a huge logistical challenge to deport millions of people at short notice. She said that "deporting just one person already entails immense effort." First, an individual "must be tracked down," and "then a lot of paperwork is necessary after the arrest, which is followed by a court decision, and then the deportation itself."
On Friday, US media reported that President Trump had ordered raids in 10 major US cities by ICE officers to deport 2,000 families.
Maureen Mayer of the human rights organization Washington Office on Latin America (WOLA) told DW: "Arresting so many people in all these cities surpasses the abilities of ICE," adding that "many of the children in these families have US citizenship."
Mayer said it was impossible to imagine what scenes would play out if parents were arrested while their children were in school, some even kindergarten. She said: "Breaking up social groups like these and separating children from their families is generally frowned upon, especially because ICE officers are known to be uncompromising."
Read more: Deal or no deal, US needs Mexicans
Separating families could hurt Trump's imageMayer notes that mass deportations of this scale could hurt Trump's bid to get reelected in 2020. "Several polls indicate that a majority of US citizens actually want to keep their country open to asylum-seekers," she said.
Andrews says that footage of deportations could harm Trump's image. She explains that "about 45% of those affected by deportations are men, and 90% of these have children who were born in the US and therefore have US citizenship." She fears that the threat of deportation would provoke heartbreaking, and potentially dangerous situations, as "these fathers would do anything, even risk their life, to stay with their children."
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