New York City, US - Until recently, Flor Reyes-Silvestre, an undocumented Mexican immigrant, had high hopes for her life in the United States.

Her political science degree was going well and with a little more schooling afterwards, she could have been on her way to a legal career.

Those ambitions came crashing down on Tuesday when US Attorney General Jeff Sessions announced the end of a programme that helped Reyes-Silvestre, 20, and other young, undocumented immigrants live and work in the US without fear of deportation.

"The reality hits you hard when you realise you might not be able to work any more," Reyes-Silvestre told Al Jazeera.

"I was thinking about law school, grad school. Now, it doesn't seem plausible to work as a lawyer or get a job at a law firm."

Nearly 800,000 young undocumented immigrants were brought to the US as children have benefited from the Deferred Action for Childhood Arrivals (DACA) programme, which has helped them gain a legal status, work permits and driving licenses.

READ MORE: 'Cruel and reckless': Trump under fire over DACA move

On Tuesday, Sessions, a Republican and longtime-critic of DACA, unveiled President Donald Trump's plans to "wind down" the programme.

DACA was introduced in 2012 by then-President Barack Obama, a Democrat, after Congress failed to agree on reforming the US' shaky immigration system.

Sessions branded Obama's carve-out a "unilateral executive amnesty" that lured a "surge of unaccompanied minors" to the southern border.

"It also denied jobs to hundreds of thousands of Americans by allowing those same jobs to go to illegal aliens," Sessions told reporters on Tuesday.

'Tall order' for Congress

The scheme does not end immediately. Congress has the next six months to find a political solution before legal protections for DACA recipients - known as "Dreamers" - are phased out.

This is widely viewed as a long shot. Legislators failed to reform the US immigration system during Obama's eight years in office, despite pressing concerns over 11 million undocumented people living in the country.

That gridlock has gotten worse since Trump came to power in January. His fellow Republicans could not agree on a healthcare overhaul earlier this year and upcoming debates on the budget and taxes look similarly dicey.

"It's going to be a tall order [for] this dysfunctional Congress to magically get its act together in the next six months and pass immigration reform," Steve Choi, director of the New York Immigration Coalition, told reporters in Manhattan on Tuesday.

Phasing out DACA does not immediately trigger the mass deportation of all 800,000 Dreamers. Instead, it is expected that they will lose that status and see work permits lapse as they revert back their undocumented status.

In a statement, Trump promised to act "with heart and compassion - but through the lawful democratic process - while at the same time ensuring that any immigration reform we adopt provides enduring benefits for the American citizens we were elected to serve".

Trump said he had advised the Department of Homeland Security that "DACA recipients are not enforcement priorities unless they are criminals, are involved in criminal activity, or are members of a gang".

On the campaign trail, Trump promised to deport all undocumented migrants. Since taking office, he appeared to soften on dreamers, a relatively well-educated and industrious group who he described as "incredible kids".

Late on Tuesday, Trump tweeted that he would "revisit this issue" if Congress fails to "legalise DACA" within six months.

But many have pushed back on Trump's comments, saying he hasn't shown compassion and has instead left the futures of hundreds of thousands of young people in legal limbo.

Support for Dreamers

Many have rallied to support the young adults who have spent much of their lives in the US.

A Morning Consult poll in April found that 78 percent of voters wanted to let dreamers stay in the US; 56 percent expressed support for eventual citizenship. Only 14 percent of respondents said they should be sent back to their countries of origin.

Dreamers, other undocumented immigrants and their supporters yelled, "Shame!" in front of the White House. And at least nine DACA recipients were arrested in front of Trump Tower in New York City on Tuesday, in advance of bigger rallies that were planned for the evening.

Supporters argue that recipients grew up and are integrated into American society, with little connection to the countries they hail from. They point to young people like Reyes-Silvestre as poster children for the benefits of foreign talent.

READ MORE: DACA scrapped - What next for 800,000 'Dreamers'?

Reyes-Silvestre arrived in the US at the age of two with her parents from Puebla, Mexico. She said she speaks Spanish and has "seen pictures" of the city where she was born, but would struggle even to catch a bus in a Mexico of which she knows little about. She calls New York her home now.

Most Dreamers came from Mexico and other parts of Central and South America. On average, they entered the US at the age of six and a half. Some 200,000 live in California; 100,000 are in Texas and 50,000 live in New York. Many also live in Illinois and Florida.

Dreamers are good for the economy, according to a study by the University of California, San Diego. Some 97 percent of DACA recipients are employed or in school. They open firms and buy cars and homes and will boost the US economy by $460bn over the next decade.

At least 72 percent of the top 25 Fortune 500 companies employ Dreamers, meaning that phasing out DACA will likely force big firms to spend time and cash recruiting new talent, Tom Wong, the author of the University of California study told Al Jazeera.

READ MORE: American dream fades for child immigrants under Trump

Jamie Dimon, the chairman and CEO of JPMorgan Chase & Co bank said in a statement that "America is and always has been a country of immigrants."

"We should do everything in our power to continue to attract the best and brightest because they make us stronger as a people and as an economy," she added.

Obama used his Facebook page to join the throng of criticism, calling Trump's move "cruel".

"To target these young people is wrong - because they have done nothing wrong. It is self-defeating - because they want to start new businesses, staff our labs, serve in our military, and otherwise contribute to the country we love," Obama said.

'We feel vulnerable'

Trump's decision indicates he is moving ahead with his campaign promises - despite his previously softened tone on DACA recipients.

It came on the same day that Republican officials from 10 states had set as a deadline for his administration to rescind the programme or allow it to face a legal challenge.

Yajaira Saavedra, 29, is another undocumented Mexican migrant who now expects her DACA status to expire in the coming months. She is less anxious than Reyes-Silvestre.

The scheme was merely a "Band-Aid" that never gave her a strong sense of security in the US, she said.

She described feeling let down by both Obama and Trump. The US government had persuaded her and many others to "come out of the shadows" and reveal their names, addresses and other personal data on DACA forms.

"The government has our records and knows where we are," Saavedra told Al Jazeera.

"We're vulnerable. Here in New York, even though it's a sanctuary city," she added, referring to cities and states that have limited their cooperation with federal immigration authorities in hopes of reducing the number of deportations.

"We're vulnerable to the NYPD [police force] and there's so much racial profiling in this country. It scares me."

Follow James Reinl on Twitter @jamesreinl