Sunday's incident, which took place in response to a group of migrants from the Mexican side rushing at the border fencing, was the latest chapter in a saga that has pitted Trump's hardline stance on immigration against thousands of migrants who have made their way north through Mexico from violent and impoverished Central American countries.
Tensions had been growing in Tijuana and Trump announced on Saturday that the migrants would have to wait in Mexico until their individual asylum claims were resolved in the United States, a significant shift in U.S. asylum policy that could keep Central Americans in Mexico for more than a year.
Trump went further on Monday, saying Mexico should send the Central Americans, mostly Hondurans, back to their home countries.
"Mexico should move the flag waving Migrants, many of whom are stone cold criminals, back to their countries. Do it by plane, do it by bus, do it anyway you want, but they are NOT coming into the U.S.A. We will close the Border permanently if need be. Congress, fund the WALL!" Trump tweeted.
Mexican government officials had no immediate response.
U.S. government agencies defended the tough response to Sunday's incident at the San Ysidro crossing south of San Diego. News pictures showing children fleeing tear gas prompted sharp criticism from some lawmakers.
Rodney Scott, chief U.S. Border Patrol agent in San Diego, said authorities had arrested 42 people. The vast majority of those assembled at the border were economic migrants who would not qualify for asylum, he told CNN, adding that there were few women and children.
The U.S. Department of Homeland Security said U.S. Customs and Border Protection officers were struck by projectiles thrown by caravan members.
Some rights advocates and legal experts were concerned that the Trump administration was seeking to use the melee to make the case for keeping the migrants out of the country rather than letting them in to request asylum.
U.S. officials reopened the San Ysidro crossing, near the Mexican city of Tijuana, on Sunday after closing it for several hours.
In Mexico, Immigration Authority Director Gerardo Garcia told television channel Televisa that 98 people had been arrested and were in process of deportation as of Sunday night.
The migrants have traveled through Mexico in large groups, or caravans. There are more than 7,000 at the U.S. border in Tijuana and the town of Mexicali, with more than 800 others still on the move toward the border.
Many of those in Tijuana have said they will wait there until they can seek asylum. If they enter the United States, legally or illegally, they have a right to seek asylum.
Trump has said the migrants should not easily enter the country and on Monday he threatened again to shut down the U.S.-Mexico border, which stretches for 2,000 miles (3,200 km).
Although Sunday's incident took place at a part of the border where there is already a physical barrier, Trump again urged Congress to fund his long-promised border wall, as well as reiterating his unsubstantiated assertion that there are many criminals among the migrants.
Mexico has been in negotiations with the United States over a possible plan to keep migrants in Mexico while their asylum claims are processed.
Tensions had been rising in recent days in Tijuana, including protests against the migrants by Mexican residents of the border city.
Authorities sent in more police to guard the crowded shelter where migrants are housed in Tijuana.
Melkin Gonzalez, a 26-year-old Honduran man, recounting Sunday's tear gas firing, said: "I fell in dirty water when I was running (away) and I still don't have any clothes to change into. Even so, I'm not going back to Honduras, I want to go to the United States."
The U.S. military said on Monday it had shifted about 300 service members from Texas and Arizona to California in the past few days.
In a statement, U.S. Northern Command said that these forces would include military police, engineering and logistics units. It added that less than 200 troops had been sent home from the border mission, meaning that in total about 5,600 troops active-duty troops are on the border with Mexico.
U.S. military officials have said they expected troops to be repositioned as the situation developed and changed.
'TEAR GASSING FAMILIES'
Democrats and other critics called the Trump administration's use of tear gas an overreaction, and questioned the idea of keeping the migrants in Mexico to make asylum claims there.
"Tear gassing families seems unnecessary," Lee Gelernt, the deputy director of the ACLU Immigrants' Rights Project, told CNN.
He told Reuters that U.S. and international immigration and asylum laws require the United States to ensure the safety of asylum seekers, so keeping them in Mexico and exposing them to drug cartels and gangs while they await a review of the asylum claims would run afoul of these laws.
Geoffrey Hoffman, a professor and director of the University of Houston Law Center Immigration Clinic that represents migrants applying for asylum, said the administration would try to capitalize on Sunday’s events along the border to push its argument that the migrants should remain in Mexico.
“However, the problem with such an approach is it demonizes immigrants who have legitimate asylum claims and violates their right to seek asylum. It is a ‘throw the baby out with the bathwater’ approach because although not everyone may have a valid asylum claim, many people do.”
Tijuana Mayor Juan Manuel Gastelum, who has said his city is facing a humanitarian crisis, told a local radio station on Monday that the United States would take 2-1/2 to three months to start processing asylum requests, meaning the some 5,200 people currently packed into a shelter in the city could wait three months for their cases to be attended to.
U.S. lawmakers face a deadline to approve funding for the federal government by Dec. 7. Trump has repeatedly threatened to shut down the federal government unless Congress pays for the wall.
Democrats want more comprehensive immigration reform in addition to additional border security, but strongly oppose Trump's wall. (Reporting by Susan Heavey in Washington and Lizbeth Diaz in Tijuana Additional reporting by Doina Chiacu and Idrees Ali in Washington and Tom Hals in Wilmington, Delaware Writing by Susan Heavey and Frances Kerry Editing by Alistair Bell and James Dalgleish)
(This story has not been edited by Devdiscourse staff and is auto-generated from a syndicated feed.)