The tear-gas confrontation between Central American migrants and U.S. Customs and Border Protection agents on Sunday ended with families fleeing clouds of the searing gas near the U.S. border with Mexico in Tijuana.
But it may have started months earlier with a policy shift.
Around April, CBP announced it was restarting a policy of "metering" asylum-seekers at the border, or only allowing migrants into the U.S. if there is sufficient room in holding facilities on the U.S. side, according to CBP reports.
That technique, used on and off again since 2016, created a backlog of migrants at the Tijuana-U.S. border that, coupled with confusion about U.S. immigration law and other factors, led to Sunday's widely televised brush with U.S. border agents.
"What happened (Sunday) was a wake-up call," said Alex Mensing, an immigrant advocate with Pueblo Sin Fronteras who has been staying with the migrants. "There needs to be a better solution than waiting in a muddy, cold camp while the U.S. decides who can accept for asylum proceedings."
The caravan of migrants, mostly from Honduras, Guatemala and El Salvador, arrived in Tijuana a few weeks ago only to find another 2,800 immigrants already there waiting for their chance to seek asylum in the U.S. The Baja California government estimates there are now nearly 7,500 migrants in the state.
About 2,000 of them remain in Mexicali, about 90 miles from the border, and continue to consider going to Tijuana.
The Mexican government has opened up Unidad Deportiva Benito Juarez, an open-air sports complex less than a mile from the border, to house the migrants, as U.S. immigration officials process around 40 asylum applicants a day. Some of the migrants have complained of a lack of food and water at the complex, as well as being exposed to rain, mud and other elements.
The issue has become highly politicized: President Trump called the migrants' acts an "invasion" and deployed military units to the border.
Over the weekend, organizers within the caravan began plotting a peaceful march to the border to shed light on their plight and urge U.S. officials to speed up the asylum process. The slowness of the process stems, in part, from the policy change in April just as a previous, smaller caravan arrived in Tijuana.
Because of the metering process, migrants are being turned away from legal ports of entry and often decide instead to cross illegally between legal entry points, according to a September report by the Homeland Security Department's Office of Inspector General.
OIG investigators interviewed two asylum-seekers apprehended by Border Patrol agents who said they had crossed illegally after initially being turned away at ports of entry and another woman who had been turned away three times by an officer on a bridge before deciding to take her chances crossing the Rio Grande.
"While the Government encouraged all asylum seekers to come to ports of entry to make their asylum claims, CBP managed the flow of people who could enter at those ports of entry through metering, which may have led to additional illegal border crossings," the report said.
Those mixed signals are sowing confusion and leading to manifestations such as the one witnessed Sunday, said Theresa Brown, director of immigration and cross-border policy at the Washington-based Bipartisan Policy Center and a former CBP policy adviser for Presidents George W. Bush and Barack Obama.
"This administration, in spite of the significant increase of asylum applications, has not increased resources to process those claims," she said. "They've increased resources to deter or prevent people from getting to the border to apply."
During a surge of unaccompanied immigrant minors in 2014, Obama administration officials opened facilities inside the U.S. to accommodate the crush of asylum-seekers as they waited for their applications to be processed.
At the sports complex Saturday, migrants gathered there painted bed sheets with signs such as "Trump We Hate You Not" or in the colors of the national flags of Honduras, Guatemala and El Salvador as they planned the march route for Sunday, Mensing said.
He and other advocates advised them not to march, warning that tension at the border was too high. But the migrants said they were desperate to shine a light on their predicament. Customs officials in San Diego said, because of the backlog, they don't expect to process any of the recent caravan members for another five to six weeks.
"If people continue to flee their home country in the conditions they're fleeing them in, this will continue to happen," Mensing said.
The march of more than 1,000 migrants started around 10 a.m. and proceeded slowly toward a bridge leading to the international crossing. Protestors waved flags from their home countries, as well as Mexican and U.S. flags, and chanted "We are not criminals! We're international workers!" and "Thank you Mexico!"
As they approached the Chaparral bridge that leads to the U.S.-Mexico border, they were met by rows of Mexican federal police dressed in riot gear. "We come in peace!" bellowed an organizer through a bullhorn. After a 30-minute stand off between police and protestors, the marchers wandered around the police then dispersed and ran toward a canal leading to the U.S. border.
The migrants -- women with backpacks, small children, young couples hand-in-hand and men covering their faces -- came to the 20-foot-high security fence separating the two countries. Just on the other side were groups of CBP agents.
When some migrants threw rocks and other projectiles at the U.S. agents and rushed a section of the barrier, the agents lobbed several canisters of tear gas and fired pepper spray to disperse the groups, according to a CBP spokesman.
"As a response to the assaults and to defuse this dangerous situation, trained CBP personnel employed less-lethal devices to stop the actions of assaultive individuals attempting to break into the U.S.," the spokesman said in a statement.
CBP agents have used tear-gas and pepper spray in the past to diffuse situations. There were 27 incidents involving tear gas in 2013 and 18 last year, according to CBP statistics. So far this year, there have been 29. Last year, CBP agents also used pepper spray in 56 separate incidents.
Sunday's incident is under review. "CBP takes Sunday’s employment of use-of-force very seriously," the statement said. "CBP reviews and evaluates all uses of force incidents to ensure compliance with policy.”
Mexican authorities arrested 98 migrants during the protests and were considering returning them back to their countries. Other migrants were debating whether they should continue waiting for their shot at asylum at the sports complex in Tijuana, or return home.
Jose Alberto Rodriguez, a migrant from Copan, Honduras, was hit with tear gas with his wife during Sunday's melee. He said he's decided to go back to Honduras rather than remain "exposed" in Tijuana.
"If we remain here, with each day we'll just end up worse," Rodriguez said.
Miguel Angel Lazo Guillen, also from Honduras, said the march was wrong-headed. He's decided to wait it out.
"It's not good to try to do things by force," he said. "I'm afraid that they will try it again and there will be people getting beaten."
Meanwhile, more asylum-seekers stream into Tijuana each day.
Contributing: Rafael Carranza of The Arizona Republic.
Follow Jervis on Twitter: @MrRJervis.