Trump wants to dramatically seal off the US-Mexico border, but White House officials reportedly think it's a terrible idea that wouldn't work

Gregory Bull, File/AP Photo

In this June 13, 2013 file photo, a US Border Patrol agent looks out over Tijuana, Mexico, by the old border wall along the US-Mexico border.

• Acting White House Chief of Staff Mick Mulvaney on Sunday said President Trump was serious in his threat to close the US border with Mexico if action is not taken to curtail illegal immigration.
• Trump said in a tweet Saturday he would order the closure of the border "for a very long time," in a move economists have warned could derail US growth prospects.
• Border and administration officials though, believe the threatened closure wouldn't work, and claim that officials have not been told to prepare for an impending closure.
• Axios reported that the widespread view in both the White House and US Homeland Security is that a total border closure is "a terrible and unworkable idea."
• Illegal immigration has been one of the flash points of Trump's presidency, with the president elected on a pledge to stop the flow of migrants into the country.

Top White House aides on Sunday claimed that President Trump's pledge to close the US border with Mexico is no empty threat - but border officials have raised questions over the government's power to make it happen.

Speaking on ABC News' This Week Sunday, acting White House chief of staff Mick Mulvaney said that it would take "something dramatic" for the president to change his mind and back down from his pledge to act in a week if Mexico doesn't step up. On Fox News Sunday White House counselor Kellyanne Conway added that the president's threat was "no bluff."

Mulvaney also reiterated Trump's pledge to cut off hundreds and millions of dollars in aid to the Central American countries of Guatemala, Honduras and El Salvador over their alleged failure to curb illegal migration.

Trump had on Saturday renewed attacks on Mexico for failing to curtail illegal immigration, and threatened to close the border "for a very long time" if the country doesn't act.

"Next step is to close the Border! This will also help us with stopping the Drug flow from Mexico!" - Trump tweeted.

AP/Evan Vucci

President Donald Trump tours the U.S. border with Mexico at the Rio Grande on the southern border.

But amid warnings from economists and political opponents that sealing off the border with the US' third largest trading partner could spell mass job losses and price hikes, border and administration officials have questioned if the order could even to put into practise.

Axios reported Sunday that the widespread view in the White House and Department of Homeland Security is that Trump's plan is "terrible" and "unworkable," while administration officials told the site it is "unlikely" Trump will follow through on his threat.

Speaking anonymously to the Washington Post, a U.S. Customs and Border Protection official said that the Trump administration had provided no details about the president's intentions and border officials had received no instructions to prepare to implement the order.

The official said that to close the border, the administration would need to notify Congress and labor unions representing border officials - measures unlikely to be completed in a week, the timeframe laid down by the president.

Other critics have pointed out that many undocumented migrants cannot be physically prevented entering the country, as they often seek out remote parts of the border to cross into US territory, where they hand themselves into border officials and claim asylum. Asylum seekers and children cannot be quickly deported from the US.

Associated Press/Russell Contreras

In this Jan. 4, 2016 file photo, a U.S. Border Patrol agent drives near the U.S.-Mexico border fence in Santa Teresa, N.M.

A senior administration official, clarifying the president's comments, told Vox on Friday that with border officials diverted from ports of entry to process undocumented migrants, the government would be forced to close those ports of entry as a last resort.

The US Customs and Border Protection did not immediately respond to a request for comment.

Illegal immigration has been one of the flash points of the Trump presidency, with the president elected to office on the back of a pledge to build a wall along the US-Mexican to curtail the flow of immigrants to the country, and accused by critics of using inflammatory rhetoric to stir up hostility to migrants.

Seeking to regain the initiative in the week following the submission of the Mueller report which allies claimed lifted the cloud of suspicion of colluding with Russia from the president, Trump on Friday was again talking tough on migration.

He claimed the US was out of detention space for undocumented migrants and threatened to close the border if two caravans of migrants made it into the US.