President Donald Trump's administration asked the U.S. Supreme Court on Monday to allow it to end a program introduced by former President Barack Obama that protects thousands of young immigrants who live in the United States without legal status.

The day before congressional elections in which Trump's harsh anti-immigration rhetoric has taken center stage, the administration urged the justices to throw out three lower court rulings that blocked Trump's plan to wind down the Deferred Action for Childhood Arrivals (DACA) program.

The policy has shielded from deportation immigrants dubbed 'Dreamers' and given them work permits, though not a path to citizenship.

In a court filing, Solicitor General Noel Francisco said the original DACA policy was introduced by Obama administration officials 'even though existing laws provided them no ability to do so.' Now, it is lawful for the Department of Homeland Security to change course, he added.

'It is plainly within DHS's authority to set the nation's immigration enforcement priorities and to end the discretionary DACA policy,' Francisco said.

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The Justice Department's move was unusually aggressive in terms of procedure, asking the justices to take action even before intermediate federal appeals courts have ruled on the three lower court rulings. The administration says a final ruling is urgently needed.

If the Supreme Court, which has a 5-4 conservative majority, agrees to hear the case, a ruling would likely come before the end of June.

Trump and his conservative political allies have made his hard-line policies toward immigration a key issue ahead of Tuesday's midterm elections that will determine if his fellow Republicans maintain control of Congress.

The Trump administration has argued that Obama exceeded his constitutional powers when he bypassed Congress and created DACA, which offers protections to roughly 700,000 young adults, mostly Hispanics.

The administration is contesting three different district court rulings from judges in California, New York and the District of Columbia that told the administration to continue processing renewals of existing DACA applications while litigation over the legality of Trump's action is resolved.

The move is the latest twist in the complicated legal battle over DACA.

President Donald Trump's administration asked the U.S. Supreme Court on Monday to allow it to end a program introduced by former President Barack Obama that protects thousands of young immigrants who live in the United States without legal status

The policy was brought in by Barack Obama in 2012 as an executive order to cover children brought illegally by their parents.

It was expanded in 2014 to cover some parents of children born in the U.S. or in the country legally, and that expansion was challenged all the way to the Supreme Court.

At the time it was lacking a judge after the death of Antonin Scalia, and had a split 4-4 decision on a bid to overturn the expansion. The effect of that decision was to keep DACA in place.

Trump promised to repeal DACA on 'day one' of his presidency, and it was eventually repealed in September 2017.

That set off immediate legal action by Democratic state governments and attorneys general meaning that there are a tranche of challenges to the Trump ruling.

One of those was brought by California's Democratic attorney general Xavier Becerra.

With a series of challenges across the country, in December 2017 the Supreme Court ruled that five cases from northern California would go to the Ninth U.S. Circuit Court of Appeals, in San Francisco, making them effectively test cases and the most advanced in the legal system.

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In January, appeals judges in San Francisco blocked the repeal - technically called rescission - pending a full judgment.

That allowed new challengers to call for DACA to go back into effect while the San Francisco court considered its fate, and in February, a federal judge in Brooklyn, New York, did that, additionally saying the program was constitutional.

That too is part of the administration's call for the Supreme Court to rule, as is a ruling by a Washington D.C. federal judge that the program should restart in full, which has not yet been implemented.

The Supreme Court put off other challenges pending the San Francisco court's decision - but now will have to rule on whether it waits for the judges or does as the Trump administration wants, and make a simple ruling itself on whether DACA is constitutional or not.

The White House has likely been motivated to move in part by the presence of Brett Kavanaugh on the Supreme Court, tilting it 5-4 conservative.

Its move comes after Trump used immigration as a key issue in the midterm elections, dispatching troops to the border and railing against the caravan in Mexico.