US President Barack Obama was to unveil measures Thursday that are expected to shield millions of undocumented migrants from deportation, as he bypasses a Congress that has failed to pass broader immigration reform.
The executive action could affect up to five million of the estimated 11 million people -- most of them from Mexico and Central America -- living and working illegally in the United States.
Since 1986, when then Republican president Ronald Reagan granted a sweeping amnesty, all attempts at major reform of the country's immigration system have failed.
In the face of congressional stalemate, Obama -- who made the issue one of his priorities upon taking office in 2009 -- has decided now, with two years left in the White House, to take the matter into his own hands.
The Democratic president will explain his proposals to the nation in a prime-time speech at 8:00 pm (0100 GMT Friday). On Friday, he will elaborate on the plan in a speech at a Las Vegas high school.
"Everyone agrees that our immigration system is broken," he said in a video message Wednesday.
"Unfortunately, Washington has allowed the problem to fester for too long."
Obama is expected to allow some migrants who have lived in the United States for more than five years, with no prior run-ins with the law, to apply for a temporary work permit.
The current program allowing temporary residency cards to minors who arrive in the United States before the age of 16 could be expanded.
All in all, the move would protect three to five million people from the threat of arrest and deportation by US federal authorities.
It may not, however, provide a clear path to eventual citizenship or permanent residency for migrants, an idea that may have to wait for another president or another generation of lawmakers.
The White House has long wanted to pass a broad immigration reform package that would offer a path to citizenship for young migrants that grew up in the United States.
A new immigration law did pass the then-Democratically controlled Senate last year, but the Republican House of Representatives blocked it and failed to agree on its own alternative proposal.
White House lawyers and many outside experts believe Obama has the constitutional authority to act.
While other presidents have used executive powers to grant amnesty to undocumented migrants, none has ever taken such sweeping action.
Republicans, who will control both the House of Representatives and the Senate in January after a huge win in this month's midterm elections, says Obama is going way too far.
"If he acts by executive diktat, President Obama will not be acting as a president -- he will be acting as a monarch," Republican Senator Ted Cruz, one of Obama's harshest critics in Congress, wrote in an opinion piece.
Some have questioned the constitutionality of his actions. Other say Congress just needs more time.
"The action he's proposed would ignore the law, would reject the voice of the voters and impose new unfairness on law-abiding immigrants, all without solving the problem," incoming Republican Senate Majority Leader Mitch McConnell said Thursday.
"It may serve him politically in the short-term, but he knows it will make an already broken system even more broken."
But Democrats counter that those same Republicans have blocked other attempts at reform.
According to an opinion poll conducted by NBC and the Wall Street Journal, 48 percent of Americans disapprove of Obama's immigration plans, against 38 percent who back them.
The political firestorm unleashed by Obama does not bode well for relations between Congress and the White House in the coming months.
Republicans cannot block a presidential decree, but they can make Obama's last two years extremely difficult -- by blocking his choices to fill ambassadorial and administration posts, as well as judgeships.
However, with the 2016 presidential election on the horizon, the debate within the party on immigration will be lively, as Republicans can ill afford to ignore Hispanic voters, 70 percent of whom voted for Obama in 2012.