WASHINGTON — President Obama suffered the biggest legal defeat of his administration Thursday when a deadlocked Supreme Court failed to revive his stalled plan to shield millions of undocumented immigrants from deportation and give them the right to work legally in the United States.

The justices’ votes were not announced, but the court’s liberals and conservatives had split at oral argument this spring. The tie means that a lower court’s decision that Obama probably exceeded his powers in issuing the executive action keeps the plan from being implemented.

President Obama: 'It is heartbreaking for millions of immigrants'

The court’s action crushed the hopes of about 4 million illegal immigrants estimated to be covered by Obama’s plan, which would have deferred deportation for those who have been in the country since 2010, have not committed any serious crimes and have family ties to U.S. citizens or others lawfully in the country.

Immigration already represents one of the flash points of the 2016 elections, with sharp distinctions between Democrats and Republicans, and the court’s action is likely to intensify the debate.

Obama responded to the Supreme Court’s news by vowing to continue other programs that put a top priority on deporting violent criminals rather than longtime residents who do not pose a threat to the country. He also sharply criticized congressional Republicans for refusing to consider his nominee to replace Justice Antonin Scalia, who died in February.

“Today’s decision is frustrating to those who seek to grow our economy and bring a rationality to our immigration system, and to allow people to come out of the shadows and lift this perpetual cloud on them,” Obama told reporters at the White House after the court announced its non-decision. “I think it is heartbreaking for the millions of immigrants who’ve made their lives here, who’ve raised families here, who hoped for the opportunity to work, pay taxes, serve in our military, and more fully contribute to this country we all love in an open way.”

He said that by refusing to vote on his court nominee, Judge Merrick Garland, Senate Republicans were “willfully preventing the Supreme Court from being fully staffed and functioning as our founders intended.”

FOUR DEADLOCKED CASES SO FAR

The inability to issue a ruling in U.S. v. Texas is the most serious consequence to date of the Supreme Court’s shorthanded status. The delay in announcing the tie – the case was argued in mid-April – indicates that the court tried to find a compromise that could draw five votes.

Supporters of the administration had hoped that at least one of the conservative justices – perhaps Chief Justice John G. Roberts Jr. – would come to their aid by saying that Texas and the other states that challenged Obama’s executive action did not have the legal standing to sue. But there was little interest in that argument when the justices considered the case.

The eight-member court has deadlocked in four cases this term and has three more to decide before it concludes its work Monday.

Left on the court’s agenda is the most important abortion case in 25 years, focused on clinic restrictions imposed by Texas that are similar to those in other states. The court is also deciding whether former Virginia Gov. Robert F. McDonnell was wrongly convicted on corruption charges for the gifts and loans he and his family received from a Richmond, Virginia, businessman.

HIGH STAKES IN NOVEMBER ELECTION

The court’s one-sentence disposition of the immigration case means that the important legal questions it raised about the extent of the president’s powers will remain unanswered for now.

The inability of the justices to reach agreement underscores the enormous significance of the November elections for the future of the Supreme Court. Even if a lame-duck Senate approves Garland’s nomination after the election – shifting the court’s ideological balance to the left – three of the court’s justices will be 78 or older when the winner of the presidential election takes office. The next president could have the chance to name more justices and recast the direction of the court.

The court’s action Thursday also means that immigration will only escalate in importance as a campaign issue.

Presumptive Democratic nominee Hillary Clinton supported Obama’s action and has said she will expand it. Presumptive Republican nominee Donald Trump has drawn a hard line on illegal immigration and would almost surely have rescinded it.

Clinton said after the court’s announcement that those whom Obama wanted to shield with his order “enrich our communities and contribute to our economy every day. We should be doing everything possible under the law to provide them relief from the specter of deportation.”

She said if elected, she would aim to expand the program, and she already has said she would pursue comprehensive immigration reform within her first 100 days in office.

REPUBLICANS CELEBRATE BIG VICTORY

Trump called Obama’s program “one of the most unconstitutional actions ever undertaken by a president.”

“This split decision also makes clear what is at stake in November,” Trump said. “The election – and the Supreme Court appointments that come with it – will decide whether or not we have a border and, hence, a country.”

House Speaker Paul Ryan, R-Wisconsin, welcomed the Supreme Court’s non-decision, calling it “a win for Congress” and for the constitutional separation of powers.

Texas Attorney General Ken Paxton, a Republican who led the states opposing Obama’s plan, said: “Today’s decision keeps in place what we have maintained from the very start: One person, even a president, cannot unilaterally change the law. This is a major setback to President Obama’s attempts to expand executive power and a victory for those who believe in the separation of powers and the rule of law.”

NO CHANGE IN DEPORTATION POLICY

The plan that Obama announced in November 2014, Deferred Action for Parents of Americans and Lawful Permanent Residents, or DAPA, would allow illegal immigrants in those categories to remain in the country and apply for work permits if they have been here at least five years and have not committed felonies or repeated misdemeanors. Obama also expanded a 2012 policy, Deferred Action for Childhood Arrivals, or DACA, which covered those brought to this country as children.

Obama stressed to reporters Thursday that the DACA program would not be affected by the outcome at the Supreme Court. “It does not affect the existing dreamers,” he said, using the term for people brought to the United States as children and covered by the program.

The president also said that “enforcement policies developed by my administration” are not affected, meaning that undocumented immigrants who have put down roots and have not committed crimes “will remain low priorities” for deportation.

Those who opposed the Obama plan noted that the president in the past had said he did not have the power to implement immigration reform on his own.

“This is a great victory for the Constitution,” said Adam Brandon, chief executive of the conservative legal organization FreedomWorks. “There are three branches of government, and each of them was intended to have equal power. There is no special clause that grants a president power when he can’t get his way.”