Migrants rushed toward the border. US authorities fired tear gas. And a volatile situation that had been simmering for weeks boiled over.
Activists, politicians and everyday Americans already are pointing to dramatic images of unrest erupting at the US-Mexico border over the weekend, offering drastically different interpretations to bolster their positions in the immigration debate.
Here's what we know about what unfolded, how we got here and what could happen next:
We've been hearing about these migrants for a while. What changed over the weekend?
What started as a peaceful march spiraled out of control.
Migrants set out toward the border Sunday morning from a sports complex in Tijuana, Mexico, where most of the them have been staying as they wait for the chance to seek asylum in the United States. Their aim, organizers had said, was a peaceful protest.
But migrants heading toward a pedestrian border crossing were met by Mexican police trying to block their path, said Wendy Fry, a reporter with the San Diego Union-Tribune who was at the scene. That, Fry said, is when the situation shifted.
"Frustrations kind of started to rise. It definitely got more heated ... and then people just started running in all different directions," Fry told CNN.
Protesters split off toward multiple locations and pushed past Mexican police, according to US Customs and Border Protection officials.
As migrants tried to cross the border, authorities on the US side used tear gas to disperse them. Video of the scene showed a cloud of tear gas that sent people running and screaming, including families with young children.
Why was tear gas used?
Immigrant rights advocates swiftly criticized CBP officials for using tear gas, especially on children. They argued that authorities had overreacted.
"The administration's use of tear gas to keep out border crossers is appalling," said Archi Pyati, chief of policy at the Tahirih Justice Center. "These are human beings who deserve to be treated with care and humanity. ... It is shocking the US has stooped this low."
But CBP officials say they had no other choice.
"The group immediately started throwing rocks and debris at our agents, taunting the agents," said Rodney Scott, chief patrol agent of the Border Patrol's San Diego sector.
Agents deployed tear gas "to protect themselves and to protect the border," Scott told CNN on Monday.
"When the threat is to our personnel or to protect others, you've got to do what you've got to do," he said. "What I find unconscionable is that people would intentionally take children into this situation."
Who are the migrants in Tijuana and why do they want to come to the United States?
Thousands of Central American migrants have arrived in the Mexican border city of Tijuana in recent weeks. They were part of so-called caravans that trekked through Honduras, Guatemala and Mexico, largely on foot, to reach the US border and seek asylum.
More than 5,600 migrants are staying in the makeshift shelter officials opened in the city's Benito Juarez Sports Complex, Mexico's Social Development Secretariat said Monday.
As CNN followed the migrants' journey, they shared a range of reasons for heading north.
Dozens of lesbian, gay, bisexual and transgender migrants were the first in this group to arrive in Tijuana. They said they were fleeing persecution in their home countries and hoped to find safety in the United States.
Many other migrants said they were escaping violence or searching for work to provide for their families. Some said they'd been deported from the US and were hoping to reunite with family members north of the border.
Trump administration officials have repeatedly characterized hundreds of migrants in the group as criminals, saying they based their assessment on intelligence sources and other methods. But they've offered little evidence to substantiate that claim.
CBP Commissioner Kevin McAleenan told reporters Monday that Mexican authorities had arrested more than 100 caravan migrants for criminal activity.
"So I think it's safe to say that there are lots of criminal elements involved in the larger group," he said.
What does it mean to seek asylum in the US? And do migrants in this group have any shot at getting it?
Asylum is a protected status that allows people fleeing persecution to live legally in another country.
But it's long been difficult to obtain. The Trump administration has been working to make it even tougher. And while each case is different, for migrants who've traveled in caravans to reach the border, the chances of winning asylum are slim.
In order to qualify for asylum in the United States, applicants must prove they have faced persecution in the past or have a well-founded fear of persecution due to their race, religion, national origin, political opinion or membership in a particular social group.
The Trump administration has been trying to overhaul how the US handles asylum, arguing that migrants without valid claims exploit loopholes to slip into the United States. Immigrant advocacy groups accuse the administration of manufacturing a crisis at the border and enacting policies that unjustly harm vulnerable people seeking safety.
Last week, a federal court blocked the administration's latest effort: a rule that aimed to prevent anyone who illegally crossed the border from seeking asylum.
But other steps the administration has taken to make it tougher to claim asylum remain in place.
For the thousands of migrants who are still waiting in border cities, it's unclear what will happen once they make their case. And it could be weeks or even months before they have a chance to do so.
What does Mexico have to say about all this, and what are officials there doing?
It's complicated. Mexico is on the verge of transferring power at the highest levels of government. President-elect Andres Manuel Lopez Obrador takes office on December 1.
On the campaign trail, Lopez Obrador said he felt that when it comes to immigration, Mexico shouldn't do the US' "dirty work."
But US and Mexican authorities have been negotiating over how to handle the recent waves of migrants. Last week, The Washington Post reported that US authorities had reached an agreement with the incoming Mexican administration that would result in migrants seeking asylum in the US remaining in Mexico while their cases are decided.
This would be a major policy shift if it occurs and would likely face swift legal challenges in the United States.
However, Olga Sanchez Cordero, Mexico's incoming interior minister, has denied that any deal has been reached, leaving many unanswered questions about what actually will happen once Lopez Obrador takes the helm.
In Mexico, public opinion over the matter has been mixed.
About half of those polled in a recent survey by El Universal newspaper said they disagreed with Mexico allowing Central American migrants to enter and giving them asylum. A third of those surveyed said undocumented immigrants should be deported immediately.
As large groups of migrants traveled through southern Mexico, many met them with donations. But Tijuana residents have been less sympathetic to the migrants.
About a week ago, protesters took to the streets there, claiming the growing number of migrants were putting the city's safety at risk.
Tijuana's mayor has been a vocal critic of the migrants and the response from Mexican federal officials, who he accused of not doing enough to help.
Could this affect President Trump's border wall plans?
Most US federal lawmakers are thousands of miles away from this rapidly developing situation. But it could have a big impact on what's happening in Washington.
Key budget negotiations are looming in Congress. Trump's push to build a border wall was already expected to be a sticking point; now both sides have fresh fuel for the debate.
Critics for weeks have accused the President of fear-mongering and trying to create a crisis at the border to win political points.
Trump is already seizing on the recent unrest to pressure Mexico and squeeze his political opponents in Washington as he demands financing for his border wall in the looming government funding showdown. At this point, it's unclear how lawmakers will respond.
Trump keeps threatening to close the border. Can he do that?
As unrest erupted Sunday, authorities closed one of the world's busiest international crossings, San Ysidro Port of Entry, to vehicle and pedestrian traffic for several hours. And Trump took to Twitter on Monday to repeat a threat he's made multiple times, warning he'd shut down the border if necessary.
Is that something he could do? In a word, yes.
But given that billions of dollars worth of freight crosses the US-Mexico border monthly, a better question might be whether the President is willing to suffer the economic consequences that could come with such a move.