Hundreds of thousands of young immigrants living in the United States illegally have willingly come out of the shadows and identified themselves to the Obama administration on the promise that they would be safe from deportation and allowed to work.
Some may now regret that decision as President-elect Donald Trump has promised to immediately scrap the programme that protected them.
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If he does, it is not clear whether he would take action against the more than 741,000 participants of the amnesty programme. But if he decides to pursue them, the government now has their addresses, photographs and fingerprints.
Nancy Villas, 20, was among the first to apply for the Deferred Action for Childhood Arrivals programme in the summer of 2012, waiting in line for hours at a sign-up site at Chicago's Navy Pier.
Since then she has been working part time at a child-care centre to pay for college classes. Now she is worried that she may eventually be forced to return to Mexico, a country she left when she was nine years old.
"I knew it was the only way to have better opportunities," Villas said. "I took the risk without thinking that somebody would want to take it away."
Potential deportations under Trump
Trump made illegal immigration the cornerstone of his campaign, promising to build a massive wall along the Mexican border and deport millions of people living in the country illegally.
Once he takes office, Trump can almost immediately rescind the promised protection and can probably make the accompanying work permits void.
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But there is little to suggest that he would move swiftly to deport participants in the programme. In a post-election interview with CBS' 60 Minutes, Trump said that he would focus initially on criminal immigrants living illegally in the US. He said that could be about two million to three million people, though that figure is probably inflated.
Mark Krikorian, executive director for Center For Immigration Studies, said the fears of participants in the programme may be overblown.
"Unless there's a crime issue, or something specific that's going to draw attention to an individual, I can't see how they'd be a priority," said Krikorian, whose think-tank describes itself as low-immigration, pro-immigrant.
President Barack Obama initiated the programme to shield young immigrants from deportation , some of whom don't even remember their native countries.
It didn't give the immigrants legal status, only "deferred action" - meaning they wouldn't face deportation while they participated. Also, there was never a guarantee that it would last beyond Obama's term as president.
Inclusion v 'illegal amnesty'
John Sandweg, who helped craft the programme, said the White House and the Department of Homeland Security considered that a future president could end it. But at the time, he said, it appeared that revoking already approved protections would be politically difficult.
"These are the kinds of kids you should bring out of the shadows," said Sandweg, a former acting director of Immigration and Customs Enforcement. "I don't think anyone envisioned a President Trump when this was created."
Trump wasn't subtle about his opposition to the programme.
He called it an "illegal amnesty" and promised to "immediately terminate" it. Since winning office, Trump has said that he will nominate immigration hardliner Senator Jeff Sessions as attorney general.
When the programme started, the Obama administration suggested that application files would not generally be used for enforcement efforts. US Citizenship and Immigration Services addressed the concern in its published "frequently asked questions", saying that information would be shared with enforcement officials only if someone "meets the criteria" for deportation proceedings.
But revoking the deportation protection would make those young immigrants almost immediately eligible to face deportation.
Sandweg said going that after participants would be a massive logistical undertaking that would only worsen backlogs in an already overburdened immigration court system in which many wait years for a final decision.
Adding about 750,000 to the court system "would do nothing for public safety," Sandweg said.