The impassioned election-year debate over President Obama’s immigration executive actions lands Monday before a short-handed Supreme Court, where justices will consider a fundamental question: how much power does the president truly have?

The justices plan to hold 90 minutes of oral arguments dealing with Obama’s bid to spare millions of illegal immigrants from deportation.

A coalition of states calls it an executive power grab. "President Obama's executive action is an affront to our system of republican self-government," said Sen. Orrin Hatch, R-Utah, who supports those states.

But the White House contends the president’s authority is clear, and the policies humane and reasonable. Obama has promoted his program as a plan to "prioritize deporting felons not families."

It’s a case that will be closely watched in an election season where Republican front-runner Donald Trump has made immigration enforcement a centerpiece of his campaign. The outcome also could have considerable bearing on Obama’s legacy, potentially determining whether his lame-duck bid to go around Congress is upheld or ruled an overreach.

At issue Monday is whether as many as 5 million illegal immigrants can be spared deportation -- including those who entered the U.S. as children, and the parents of citizens or legal residents. The programs -- known as Deferred Action for Parents of American Citizens and Permanent Residents (DAPA) and Deferred Action for Childhood Arrivals (DACA) -- effectively went around the Republican-led Congress.

Opponents, including 26 states and GOP members of Congress, say the plan exceeds constitutional power. 

A federal appeals court earlier had struck down DAPA, which has yet to go fully into effect. The Justice Department then asked the high court for a final review, in what could be a key test of Obama's executive powers his last year in office.

The decision to review the case was welcome on both sides of the aisle.

"The Constitution vests legislative authority in Congress, not the president,” said Hatch, urging the justices to rule against the administration. 

But the White House voiced confidence the policies would be upheld.

"Like millions of families across this country -- immigrants who want to be held accountable, to work on the books, to pay taxes, and to contribute to our society openly and honestly -- we are pleased that the Supreme Court has decided to review the immigration case," spokeswoman Brandi Hoffine said.

The issue of illegal immigration has taken a center-stage role in the Republican primary battle, as Trump calls for a border wall between the U.S. and Mexico and candidates spar over who is toughest on the issue.

The immigrants who would benefit from the Obama administration's plan are mainly parents of U.S. citizens and lawful permanent residents. Solicitor General Donald Verrilli Jr. said in a court filing that allowing the past rulings to stand would force millions "to continue to work off the books.”

Besides immigration, Obama has used his unilateral authority to act on such hot-button issues as gun control, health care and global warming.

However, as with other high-profile Supreme Court appeals this term -- on ObamaCare, abortion rights and affirmative action -- the outcome here likely will be affected by death in February of Justice Antonin Scalia, which left a 4-4 bench split along conservative-liberal lines.

A 4-4 ruling would effectively scuttle the issue until after Obama leaves office in nine months, and mean at least a temporary setback to his domestic policy legacy -- even if the justices punt, and choose to reargue the case when Scalia's replacement is sworn in. The justices also could rule narrowly on procedure, finding a compromise on a technical issue not directly related to the larger policy questions.

On the legal side, the GOP-controlled House filed an amicus brief supporting the states, telling the high court, "the Executive does not have the power to authorize -- let alone facilitate -- the prospective violation of the immigration laws on a massive class-wide scale."

Supporters of the administration vow this issue will resonate in an election year.

"There are millions of families of U.S.-born citizens that live under the fear of separation and deportation," said Ben Monterroso, executive director of Mi Familia Vota, an Hispanic advocacy nonprofit. "Our community is watching and will hold accountable those who have stood on the way of our families through the ballots in November."

MFV and other immigrant rights advocates plan to march at the Supreme Court around Monday's arguments.

The case is U.S. v. Texas (15-674). A ruling is expected by late June.