Trump pledges asylum crackdown, tent cities; is it legal?

In this photo provided by the U.S. Air Force, soldiers from the the 89th Military Police Brigade, and 41st Engineering Company, 19th Engineering Battalion, Fort Riley, Kan., arrive at Valley International Airport, Thursday, Nov. 1, 2018, in Harlingen, Texas, to conduct the first missions along the southern border in support of Operation Faithful Patriot. The soldiers will provide a range of support including planning assistance, engineering support, equipment and resources to assist the Department of Homeland Security along the Southwest border. (Alexandra Minor/U.S. Air Force via AP)

Erlin Troches, a 43-year-old Honduran migrant from the city of Santa Barbara, carries an image of the Virgin of Guadalupe that was given to him by a priest in southern Mexico, as he walks along with a thousands-strong caravan of Central Americans hoping to reach the U.S. border moves, outside Juchitan, Oaxaca state, Mexico, Thursday, Nov. 1, 2018. Troches plans to carry the religious icon with him on the entire journey, saying she symbolizes “trust, faith, and hope” that he will make it to the U.S. border. (AP Photo/Rebecca Blackwell)

President Donald Trump boards Air Force One for a campaign rally in Columbia, Mo., Thursday, Nov. 1, 2018, in Andrews Air Force Base, Md. (AP Photo/Evan Vucci)

WASHINGTON — President Donald Trump said Thursday he plans to sign an order next week that could lead to the large-scale detention of migrants crossing the southern border and bar anyone caught crossing illegally from claiming asylum — two legally dubious proposals that mark his latest election-season barrage against illegal immigration.