A man sits as cars queue up in multiple lines waiting to be inspected by U.S. border patrol officers to enter from Mexico into the U.S., at the San Ysidro port of entry, in Tijuana, Mexico, April 3, 2019.
A man sits as cars queue up in multiple lines waiting to be inspected by U.S. border patrol officers to enter from Mexico into the U.S., at the San Ysidro port of entry, in Tijuana, Mexico, April 3, 2019.

President Donald Trump on Thursday retreated from his threat to immediately close the U.S. southern border with Mexico to thwart illegal migration, instead telling Mexico it has a year to curb the flow of illicit drugs and surge of migrants to the United States or he would impose tariffs on cars it was exporting to the U.S.

Trump backed off days of Twitter comments saying he was about to close the border after White House economic advisers and Republican lawmakers warned him that closing the border would significantly affect the U.S. economy, the world's largest.

White House officials had tried to figure out a way that Trump could halt undocumented immigrants from entering the U.S. while not obstructing the flow of nearly $1.7 billion of goods and services crossing the border each day, along with nearly a half-million legal workers, students, shoppers and tourists.

Trump told reporters at the White House that Mexico "could stop" migrant caravans from the Central American countries of Guatemala, Honduras and El Salvador "right at their southern border" to halt their passage through Mexico to the United States.

U.S. President Donald Trump
U.S. President Donald Trump speaks during a meeting in the Cabinet room at the White House in Washington, April 4, 2019.

After often attacking Mexico as doing "nothing" to stem the surge of migrants heading to the U.S., Trump in recent days praised the southern U.S. neighbor for getting tougher in stopping them before they could get to the U.S. to file for asylum protection.

As for Mexico's future action against migrants, Trump said, "If they don't do it, we'll tariff the cars."

He said Mexico has a "one-year warning to stop incoming drugs; otherwise we'll close the border."

Trump's walk-back on immediately closing the border was his second retreat on a major policy issue in the last week.

A week ago, he said Republican lawmakers would adopt a new plan to repeal and replace the national health care policies that were the signature domestic legislative achievement of his Democratic predecessor, former President Barack Obama.

But when Trump's legislative supporters in Congress said they had no intention of considering a new health care overhaul before the 2020 presidential election 19 months from now, the president changed his mind and said there would not be a health care vote until 2021, by which time he hopes to have won a second term in the White House.

Some of Trump's most ardent supporters defended his call for closing the U.S.-Mexican border this week, but lawmakers who normally back his policies were not among them.

"Closing down the border would have a potentially catastrophic economic impact on our country," Senate Republican leader Mitch McConnell said. "I would hope that we would not be doing that sort of thing."

Economists outside the government also predicted economic havoc, with Mark Zandi, the chief economist at Moody's Analytics, saying "a full shutdown of the U.S.-Mexican border of more than several weeks would be the fodder for recessions in both Mexico and the U.S."