President Donald Trump's threat to close the southern border was met with criticism and concern from politicians, activists, the public—and Pope Francis. 

Trump is taking the action, he said, because of what he believes is a crisis in drug smuggling and human trafficking.

In remarks to reporters Sunday on the papal plane en route from Morocco to Rome, Pope Francis said that Trump—and people who think the way the U.S. president does about migrants—are ultimately trapping themselves in an inhumane situation. 

"Builders of walls, be they made of razor wire or bricks, will end up becoming prisoners of the walls they build," the pope said. 

The comments preceded a tweet made by the pope Saturday in which he celebrated the rights of migrants to self-determination.

"Every human being has the right to life, to dream and to find his or her rightful place in our 'common home!'" posted the pontiff. "Every person has a right to the future."

The measure to close the border comes as the administration plans to cut aid to Central American countries—a move that experts argue is almost certain to increase, not curtail, the number of immigrants at the border. 

Acting Chief of Staff Mick Mulvaney, speaking to ABC News anchor Jon Karl Sunday, said that unless "something dramatic" changed, the closure would happen this week.

Mulvaney pushed back on the idea that an increase in aid would lead to lower numbers of people on the border in an interview with CNN's Jake Tapper, also aired Sunday. 

"If we're going to give these countries hundreds of millions of dollars, we would like them to do more," said Mulvaney. "If it's working so well why are the people still coming?"

Whether or not Trump actually goes through with his threat is, as with most actions the president proposes, an open question. Rep. Tom Kole (R-Okla.) told MSNBC's Hallie Jackson Monday that Trump may be bluffing. 

Democrats took a hard line against the proposal. 

"It is actions like these in which the president is announcing a potentially devastating action to close the border for the state of Texas and the economic well-being for the nation," Rep. Sheila Jackson Lee (D-Texas) said in a tweet thread.

"Such actions will backfire," Lee continued, "cause greater pain to countries and do nothing to stop the flow of desperate migrants."

"We need a real immigration policy from this White House," added Jackson Lee.

Rep. Juan Vargas (D-Calif.) was more blunt. 

"Millions of people would ultimately lose their jobs," said Vargas. "It's really dumb."

Some critics took a broader view of the action and said it might indicate something more unsettling: a new push for authoritarianism from the president. 

"I studied democratization in college, which means I learned a lot about dictators and autocrats," said Kelly Crowley. "They always eventually close the borders."

"This guy isn't into democracy," Crowley added. "He's checking all the boxes."

Shutting down the border is "exactly the sort of move many in the GOP have—before Trump—admired in European autocrats like Viktor Orban," said Sarah Posner, a reporter with Type Investigations, referring to the far right Hungarian leader.

Trump's motivation may be even baser than that, said Philadelphia Enquirer columnist Will Bunch—the president may be doing nothing more than creating a crisis on the border to help him win reelection. 

"Trump's brand is crisis," wrote Bunch, pointing to the myriad ways the president has presented the country's woes in ways that recall "carnage" rather than hope in the first two years of Trump's administration. 

"Nothing aids the president's goal of portraying himself as a defender against invading hordes than images of large crowds of asylum seekers," said Bunch.