He's threatened to withdraw all aid from Honduras and Guatemala if they don't start dealing with the mass of migrants that have been illegally entering the United States in recent years, and said he would send the US military to America's southern border if this particular caravan was able to reach it.
Where easily 3,000 people were on the bridge the previous day, the crowd thinned out considerably Saturday.
But the pace was slow, conditions hot and uncomfortable, and patience wearing thin.
Those on the bridge watched with desperation Saturday as workers began erecting tall steel riot barriers.
The women ran forward when immigration officers unchained a gate that had been pinning back migrants at the crossing.
Twenty-year-old Scarleth Cruz hoisted a crying, sweat-soaked baby girl above the crowd.
Cruz was among the many who appeared willing to accept any kind of migratory relief Mexico might offer. She said she had volunteered to make the journey on behalf of her family, and send money home from working in the US.
"I don't know what happened, I thought we were going to cross peacefully and then suddenly there were rocks flying and tear gas", she told AFP. The majority seek to use the country's northern border to infiltrate the USA illegally, according to the Associated Press. None were visibly detained despite the presence of hundreds of police lining the bridge.
Thousands of migrants attempted to cross the border from Guatemala into Mexico this week. They were rafted to safety in on the Mexican bank.
Mexican authorities are particularly wary of migrants attempting to cross the Suchiate River that forms the southwestern border with Guatemala, a popular illegal route into Mexico. "There is a lot of disorder", said Rivera, who was hoping to get on a bus back to Honduras laid on by the Guatemalan government.
Dozens of Arizona National Guard members were among those deployed to the border.
"On Thursdays I paid the 18th Street gang, and on Saturdays the MS-13", Aguilar said. That's a significant amount in low-wage Honduras.
In recent days Mexican authorities have made a point of showing they were stepping up security near the country's southern border.
Mexican workers handed food bottled water to the migrants on the bridge.
Organizers of a caravan of migrants trying to cross into Mexico and ultimately the USA appear intent on avoiding a repeat of a rush on the border with Guatemala that ended when Mexican security forces with riot shields and pepper spray drove them back.
Mexican President Enrique Pena Nieto said the border clash was "unprecedented" and accused some of the migrants of attacking police. "These are tough, tough people and I don't want them in our country".
He thanked Mexico for blocking the caravan's progress.
He said that he makes 150 lempiras a day, or about $6 U.S., and has no work benefits.
Trump, who ran in 2016 promising to tighten United States immigration laws end the inflow of people entering the country illegally, has called for cutting off foreign aid to Guatemala, Honduras and El Salvador if they do not stop the migrants.
Brown stressed that the caravan, "whatever its political message or design, is just a continuation of what seems to be a relatively permanent shift in migration patterns at the U.S. -Mexico border, and a large regional migration crisis, driven by violence, crime and poverty that is not going to end soon".
Their journey of almost 4500km - mostly on foot - began in San Pedro Sula, Honduras, last Friday.
Mexico says the migrants will be processed and that those without a legitimate case to travel onwards or stay in Mexico will be returned to their countries of origin.
Emigrants from those states now make up the bulk of migrants caught trying to enter the USA illegally every year.
Thousands of migrants slept - or tried to sleep - outdoors overnight underneath tarps and what blankets were available. Some of them talked among themselves.
Jose Yanez, said he woke at 5 a.m. with a backache after having nothing to cover himself from the nighttime chill.