Here is a primer on the migrant caravan arriving in the U.S. from South America and how the Trump administration is handling the situation.
Why is a caravan of migrants headed to the U.S. border?
After traveling for more than a month from Central America, about 400 migrants have begun arriving at the U.S.-Mexico border in Tijuana. They plan to seek asylum in the United States, said Irineo Mujica, the director of Pueblo Sin Fronteras, the Mexico-based group that organized the caravan. Another 300 migrants traveling with the group plan to remain in Mexico. The caravan has triggered vitriol from U.S. conservative media outlets, the White House and many Trump supporters, who see it as a mass effort to illegally cross into the United States.
Most of those seeking asylum are women and children from Honduras — including 70 to 80 infants — who advocates say are fleeing violence and instability following contentious presidential elections. Some are also from El Salvador, which like Honduras has one of the world's highest murder rates. All of the cases have been reviewed by lawyers. "They're people who have suffered," Mujica said.
What does it mean to seek asylum?
Asylum is a long-standing protection for people fleeing dangerous conditions in countries around the world. The U.S. Refugee Act of 1980 says that a person may seek asylum if they are in the United States or at its border. Asylum seekers must have a well-founded fear of persecution because of their race, religion, nationality, political opinion or membership in a particular "social group," a broad category that has included domestic violence victims and others.
Foreigners can seek asylum in two ways, affirmatively through the Department of Homeland Security and defensively, as part of fighting deportation proceedings in the U.S. Justice Department's immigration courts. Asylum seekers are screened and have their backgrounds checked and, depending on how they entered the country, may be detained pending a hearing.
In October, the White House said there were 270,000 affirmative asylum cases awaiting action by U.S. Citizenship and Immigration Services, which is part of the Homeland Security agency, and 250,000 cases pending in the immigration courts.
Is this caravan something new?
No. Pueblo Sin Fronteras (not to be confused with the Washington nonprofit People Without Borders) said it has been organizing caravans since 2008. Past caravans aimed to call attention to problems with Mexico's asylum system and treatment of migrants in Mexico, which also has deported thousands of Central Americans.
This year's was the largest caravan yet. At its peak, more than 1,000 people were walking north through Mexico. In early April, after scathing tweets from the U.S. president, organizers said the group had become so big that it was unwieldy and would end its journey in Mexico City rather than continuing to the border. But the smaller group did not disband and has begun arriving on buses at the border city of Tijuana.
Why is President Donald Trump so upset about it?
Trump and other Republicans view the caravan as an assault on border security and U.S. sovereignty. Since "Fox and Friends" reported on the caravan early this month, the president has repeatedly tweeted about it and called for the National Guard to help secure the Mexican border.
Attorney General Jeff Sessions has called the caravan "a deliberate attempt to undermine our laws and overwhelm our system," and said the Justice Department would prosecute smugglers and anyone who commits fraud. Critics of the caravan contend that most migrants are driven not by a need for asylum but a desire to find better jobs and lives in the United States. Asylum seekers are typically issued work permits while they wait for their cases to be adjudicated.
Has the Trump administration changed the asylum process?
Past presidents also have sought to limit illegal border crossings. But Trump has made the issue a top and contentious priority, framing it as a dire security concern and using language far more volatile than his predecessors.
Caravan organizers say Trump has made it harder for migrants to seek asylum by threatening to detain foreigners seeking the protection, and in some cases turning immigrants back at the border or jailing them for months. They say the Trump administration also has created a false perception that asylum seekers are fraudsters and criminals and that asylum laws are "loopholes" that should be closed.
Mujica said the people seeking asylum in the caravan are bona fide cases. Some people who started out in the caravan already have successfully sought asylum and are now in New York, Wisconsin and Texas, he said.