In a series of tweets fired off Thursday morning, President Donald Trump delivered his most extreme threat yet to the governments of Mexico and Central America: “If they don’t stop a caravan of Hondurans trying to reach the U.S. to apply for asylum, he vowed to
use the U.S. military to "CLOSE THE SOUTHERN BORDER!"
It’s unclear whether Trump is seriously considering a complete closure of the 2,000-mile border with Mexico, or if he’s using the threat simply to get America’s southern neighbors to cooperate, or that
he’s just trying to rally his political base less than three weeks before the midterm elections.
But if sealing the border is realistically on the table, then that raises countless questions over the authority of the president to do so, the logistics of such an endeavor, and the widespread consequences it would have on Americans’ ability to trade, travel and even eat.
"A shutdown of the border, even for a temporary period of time, would have dramatic and devastating economic consequences," said Peter Boogaard, a former Homeland Security official in the Obama administration now working for FWD.us, an immigration advocacy group.
The first question, whether Trump can close the border, is a simple one to answer: yes.
"You can certainly stop entries coming across the border, whether its truck traffic or cars or pedestrians," said Gil Kerlikowske, former commissioner of U.S. Customs and Border Protection. "Logistically, that's possible. The gates are closed, and you say, 'Right now we're not taking entry.'"
Previous examples are rare. President George W. Bush partially closed the southern border following the 9-11 terrorist attacks, requiring full inspections of every incoming pedestrian and vehicle that led to days-long waits. President Ronald Reagan temporarily closed ports of entry along the southern border in 1985 following the kidnapping and murder of a DEA agent in Mexico.
The situation gets more complicated if Trump is contemplating using active-duty members of the military to help seal off the massive sections between those ports of entry, a 2,000-mile stretch from Brownsville, Texas, to San Diego, Calif.
The National Guard can definitely be deployed inside the U.S. Several presidents have done so, mobilizing those to assist along the southern border, respond to natural disasters, and help in the war on drugs. Trump has already done the same, issuing an order in April that sent 2,100 National Guard troops to help stop what Trump describes as a “crisis” level of illegal immigration.
But it's less clear if a president can order active-duty members of the Army, Navy, Air Force and Marines to patrol the southern border.
The Posse Comitatus Act of 1878 bars active duty military troops from performing domestic law enforcement functions. Legal and military experts have long cited that law as a barrier to domestic deployments of the military.
"The Department of Defense really doesn’t like to use the military in this law enforcement role. It blurs the line," said Christine Wormuth, a former undersecretary at the Defense Department and now director of the International Security and Defense Policy Center at the Rand Corporation. "The United States public doesn’t want the military to be policemen."
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