President Donald Trump on Tuesday ended an amnesty for 800,000 people brought to the United States illegally as minors, leaving their future in serious doubt and triggering a political firestorm.
The US leader -- who had promised to end the Obama-era program "with great heart" -- ordered a phase out of an amnesty for those brought to the United States under the age of six, many of whom know no other country.
The so-called "Dreamers" now have between six months and just over two years until they become illegal US residents and subject to potential deportation.
Defending his decision -- which drew blowback from across the political spectrum as well as from rights groups and business leaders -- Trump argued that the amnesty implemented by Barack Obama was an unconstitutional overreach of presidential powers and would likely be struck down by the courts.
He urged Congress to use the six month grace period to put a lasting solution in place -- something lawmakers have tried and failed to do for decades.
"I am not going to just cut DACA off, but rather provide a window of opportunity for Congress to finally act," said the president, who ran on a hard-right immigration and law and order platform and painted his decision as an effort to put natural-born Americans first.
"In June of 2012, President Obama bypassed Congress to give work permits, social security numbers, and federal benefits to approximately 800,000 illegal immigrants currently between the ages of 15 and 36," Trump said.
"Before we ask what is fair to illegal immigrants, we must also ask what is fair to American families, students, taxpayers, and jobseekers."
Obama introduced the program known as DACA, or Deferred Action for Childhood Arrivals, in 2012, after efforts to pass legislation failed. 
Around 800,000 people took up the offer to get two year renewable permits, but a similar number opted to stay in the shadows largely because of uncertainty over policy once Obama left office.
Senior Department of Homeland Security officials admitted that the addresses and other information provided by current permit holders would be kept on record indefinitely.
But, one official said, there was "no plan at this time" to specifically target recipients for deportation.
- 'Cruel. Not America' -
Trump's decision was met with widespread condemnation. 
"I'm a human and I'm part of this society," said 28-year-old Greisa Martinez Rosas, who was born in Mexico, but now lives in Dallas and fears a return to legal limbo.
"My parents are undocumented and living like that is not normal. You are hunted by ICE agents, deportation agents and by police. You can't do the things normal people do," she said while protesting in front of the White House.
Former Vice President Joe Biden joined figures as diverse as the Mexican government and trade unions in condemning Trump.
"Brought by parents, these children had no choice in coming here. Now they'll be sent to countries they've never known. Cruel. Not America," Biden tweeted.
Opponents hinted that they may challenge Trump's decision in the courts. "We warned you not to threaten our neighbors, @realDonaldTrump. New York City will fight to defend our Dreamers," said New York Mayor, Bill de Blasio.
- 'Part of this great country' -
Even Trump allies in business and the Republican party voiced concern, arguing the policy would damage the economy and was not in keeping with US values.
"To reverse course now and deport these individuals is contrary to fundamental American principles and the best interests of our country," the American Chamber of Commerce said in a statement.
"With approximately 700,000 DACA recipients working for all sorts of businesses across the country, terminating their employment eligibility runs contrary to the president's goal of growing the US economy."
Much of the business world, especially the high-tech firms of California's Silicon Valley, stood firmly against a DACA repeal. The program offers the equivalent of a renewable residence permit to young people who were under the age of 16 when they arrived and have no criminal record.
Top congressional Republican Paul Ryan called on lawmakers to step in.
"It is my hope that the House and Senate, with the president's leadership, will be able to find consensus on a permanent legislative solution that includes ensuring that those who have done nothing wrong can still contribute as a valued part of this great country," he said in a statement.
The chances of a badly divided Congress reaching a long-elusive agreement on immigration reform in months appear dim.
Several Republican lawmakers had warned Trump against cancelling the popular program.
Trump himself has publicly agonized and wavered over the fate of the young immigrants, declaring in the Oval Office last week: "We love the Dreamers."