Migrants sleep packed together in a church courtyard at nightfall, as a thousands-strong caravan of Central Americans hoping to reach the USA border stops for the night in Niltepec, Oaxaca state, Mexico on October 29, 2018.
A caravan in the spring ultimately fizzled to just about 200 people who reached the USA border at San Diego.
But Trump, who stoked anger and fear over illegal immigration on his way to winning the 2016 presidential election, has seized on the caravan at campaign rallies ahead of next week's midterm polls, hoping the issue will again fire up his core support.
On Saturday, an arm of the Mexican federal government for the first time seemed to be directly helping the migrants advance: Grupo Beta, Mexico's migrant protection agency, gave rides to stragglers and passed out water.
But Mexican officials seem intent only on seeing the caravan melt away as it travels toward the USA border.
The Pentagon said it's sending 5,200 troops to the Southwest border in an extraordinary military operation.
US officials have stressed that the troops would not police the border and instead carry out support roles like building tents and barricades, and flying USA customs personnel to locations along the border.
"This is an invasion of our Country and our Military is waiting for you!"
Luis Acosta holds 5-year-old Angel Jesus, both from Honduras, as a caravan of migrants from Central America en route to the United States crossed through the Suchiate River into Mexico from Guatemala in Ciudad Hidalgo, Mexico on October 29, 2018.
In April, Trump ordered up to 4,000 National Guardsmen to head to the border as a different migrant caravan wound its way north.
"This is inhuman. If a child had been left in the middle of that mess they would have killed them", a migrant in the group, which is estimated to number between 1,500 and 2,000, said.
"I think they are risking much to cross to this side", Rodriguez said.
"We go for about a month, I stopped counting the days, we are helped by Almighty God and the good people you meet on the way", says this mother of a family.
When asked if the US military was being used as part of a political stunt, O'Shaughnessy noted that the USA military routinely partners with the Department of Homeland Security on a host of operations.
United States Northern Command and North American Aerospace Defense Command General Terrence John O'Shaughnessy.
The group promoting the caravan, Pueblo Sin Fronteras, wants a meeting with Mexican authorities in the capital city to discuss migrants' rights and how to handle the caravan moving forward.
That's because the military is bound by the Posse Comitatus Act, a 19th- century federal law that restricts participation in law enforcement activities.
Asked about the use of weapons, O'Shaughnessy said the active-duty troops have been given clear guidance on the use of force and there will be unit and individual training to make sure they know what they can and can't do. The official said the deployment is being done to support the Department of Homeland Security and Customs and Border Protection. Only about 200 in that smaller group made it to the border.
The troops will provide "mission-enhancing capabilities" at ports of entry in Texas, Arizona and California, officials added, and will be armed.
While the majority of the caravan rested and reorganized in Tepanatepec, Mexico, a group of a few hundred trekked through the Guatemalan border town of Tecun Uman.