The first, largest group of nearly 4,000 entered nearly two weeks ago and is now in Donaji, Oaxaca.
Since the migrants have a case as asylum-seekers, the suit argues, Trump's vow to effectively turn them away at the border is a violation of their due process rights under the Constitution. So far, it is not certain whether any operative suffered any injury but Guatemalan officers were hurt.
Asked if he envisions United States troops firing on anyone in the groups of migrants, Trump told reporters at the White House: "I hope not".
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But U.S. President Donald Trump ramped up his pre-election focus on the caravan and others behind it, talking of creating a U.S. military force on the border that would outnumber the migrants, many of them women and children. "We're going to consider - and I told them consider it a rifle. They want to throw rocks at our military, our military fights back", Trump said during a White House press conference about immigration. "Within that flow and included are about 17,000 criminals past year along with hardened smugglers and people from over 100 different countries around the world".
The governor of the Mexican state of Veracruz, Miguel Angel Yunes, said on Friday buses would be provided to carry migrants to the nation's capital.
Retired Lt. Gen. Jim Dubik, who oversaw the effort to build the Iraqi army and police, said that Trump's description of the migrant caravan as an "invasion" was wrong. The migrants are still more than 1,000 kilometers (more than 620 miles) from the US, a distance that will likely take several weeks for them to walk.
"The challenge with the caravan is it's a very amorphous concept, you don't get a ticket to the caravan, it's not a membership program", Nielsen said. Trump has repeatedly addressed the issue of who exactly is included among the thousands of caravaners, including in a series of tweets Wednesday.
But it remains unclear how many people now en route to the USA will even make it to the border.
The setback comes days after caravan leaders asked for "safe and dignified" transport to Mexico City, a checkpoint along the way for a group that has been dwindling in size as members either apply for protected status in Mexico or drop out over fatigue exacerbated by the sweltering weather conditions they have been facing. "For that reason, we also offered them transportation so that, if possible, tomorrow. they may be able to go to Mexico City or to the place they wish". That group includes Hondurans, Salvadorans and some Guatemalans.
The public criticism from former military officials raised questions about why the president had chose to dispatch such a large force on such short notice days before a critical election.
The US President has already attacked undocumented immigrants ahead of next week's mid-terms by announcing plans to send at least 5,200 active-duty troops ― and possibly as many as 15,000 ― to the southern border to address migrant caravans, which are now 900 miles away.
Notably, he said his executive order would come next week, which means it could be after Election Day.
Trump has rejected the idea he has been "fearmongering" and using the issue for political purposes, but his escalating rhetoric in the final days of the campaign season calls that denial into question.