Trump threat to close southern border legally 'murky'

U.S. President Donald Trump could be entering "murky" legal territory if he attemptedto close down the southern border with Mexico, a move that some observers saycould have significantimpacts on both economies.

"The implications are pretty grave," saidJock O'Connell, a California-based internationaltrade adviser.

On Friday, Trump, via Twitter,threatenedto close the U.S. southern border if Congress continued to refuseto provide more than$5 billion US in taxpayer funds for his promised wall along the border with Mexico. The disagreement has led to the continuedpartial government shutdown.

"We will be forced to close the Southern Border entirely if the Obstructionist Democrats do not give us the money to finish the Wall & also change the ridiculous immigration laws that our Country is saddled with," Trump tweeted.

'It's very murky'

Trump has threatened to shut down the southern border before.Andwhat he means by closing it down "entirely" and what legal authority he would have to shut down the border is not entirely clear.

"It's very murky," saidStephenLegomsky, professor emeritus at Washington University's law school.

Trump has discretion to decidewhich ports of entry should be established and closed. That is determined by administrative regulations, allwithin the control of the executive branch of the U.S.government, he said.

Last month, for example, U.S. officials temporarily suspended traffic in both directionsat the San Ysidro port of entry between San Diego and Tijuana, disrupting trade at the most heavily trafficked land border in the Western hemisphere.

But ifTrump wanted to close all ports of entry, he might becontraveningCongress's general intention to set up a particular system for implementing immigration laws, said Legomsky,theformer chief counsel of U.S. Citizenship and Immigration Services in the Department of Homeland Security.

"I don't think the president could get away with shutting down all ports of entry," he said. "At some point there has to be a line drawn where if you cross that line you're really undermining the whole system of immigration set up by Congress."

Invoking national security

Both Legomskyand O'Connell suggested that Trump would have a stronger case by invoking"national security" as the rationale to close down the border

And he would likely doubledown on his claims thatthe borders are beingoverrunby adisproportionatenumber of violent streetgangs andIslamicterroriststo justify such action.

"If he leans on national security as the rationale for that action thenhe most likely has the authority to close down the borders,"O'Connellsaid.

"He could do it indefinitely as long as he insists that there is a clear national security implication involved."

Legomskyagreed that Trump's invocation of national security, justified or not,would make it harder for the court to set aside his actions

"I just don't know whetherthe court would be quite willing to accept national security at face value," he said.

The courts, he said, might agree that it'spossible somebody could come across the border and threaten our national security. But they also might question whether Trump hasto shut down all ports of entry in order to prevent that action.

If Trump was able to get his way, and shut down the border, it could result in losses of billions of dollars,said Duncan Wood, director of the WilsonCenter'sMexico Institute.

Mexico is the United States's third-largest trading partner. In 2017, the U.S exported $243 billion in goods to Mexico, and imported $314 billion worth, accordingto the U.S. Census Bureau.

Mexico depends on the U.S.for 80 per cent of its exports and would "be hit very, very hard" by a border shutdown, Wood said. "It would cause a very significant and negative impact on the Mexican economy."

Aswell, the U.S. economy, which depends less on Mexico, would still be "hit really, really hard," he said.

But it's not just the importers and exporters that would suffer impacts from a border shutdown. Blue-collar workers who work for the warehouses and distributioncentres, drive the trucks andthe trains that move goods across the border would beimmediately vulnerable to any trade disruption, O'Connell said.

"So the first people to get laid off are going to beliterally armies of blue collar workers," O'Connell said.

Intensify inspections

If not a complete border closure, Trump might also be able to gum it upby ordering the customofficers to intensify their inspections.

"[They]could simply stop every truck and create colossal traffic jams and in effect achieve his purpose that way,"O'Connellsaid."Not through necessarilyordering a border closing, rather like closing down the border by essentially making it exceedingly difficult for traffic to move."

Searches onevery vehicle, every person crossing the border would be a nightmare, with trucks and cars lined up for hundreds of kilometres, Wood said.

"Commerce between the two nations would grind to almost a halt."