The 4-4 split on the Supreme Court could favor opponents of Obama's immigration executive orders, as a tie vote would uphold lower court rulings that viewed the orders as unconstitutional.

In 90 minutes of arguments, the court appeared to break along ideological lines, with the four liberals supporting the president and four conservatives voicing skepticism.

Yahoo News:

In order to win, Obama would need the support of one of the court's conservatives, most likely Chief Justice John Roberts or Anthony Kennedy. But they both at times hit the Obama administration's lawyer, U.S. Solicitor General Donald Verrilli, with tough questions.

Kennedy expressed concern that Obama had exceeded its authority by having the executive branch set immigration policy rather than carry out laws passed by Congress.

"It's as if the president is setting the policy and the Congress is executing it. That's just upside down," Kennedy said.

A ruling is due by the end of June.

Obama's plan was tailored to let roughly 4 million people - those who have lived illegally in the United States at least since 2010, have no criminal record and have children who are U.S. citizens or lawful permanent residents - get into a program that shields them from deportation and supplies work permits.

Obama said the program, called Deferred Action for Parents of Americans and Lawful Permanent Residents (DAPA), was aimed at preventing families from being torn apart.

The case comes during a heated presidential campaign in which the status of the roughly 11 million immigrants in the United States illegally, most of them from Mexico and other Latin American nations, has been a central theme. Immigration is also a global concern, with Europe now struggling with a flood of immigrants fleeing violence in Syria, Iraq and elsewhere.

The Republican-governed states that filed suit asserted that the Democratic president overstepped his authority provided in the Constitution while his administration said he merely provided guidance on how to enforce deportation laws.

A 4-4 ruling is possible because there are only eight justices following February's death of conservative Antonin Scalia.

But nothing is certain in this Roberts court, and some legal experts have raised the possibility of a compromise:

One possible compromise outcome would be that the court could uphold Obama's plan in part while leaving some legal questions unresolved, including whether the government can provide work permits to eligible applicants.

In this compromise, the court may recognize President Obama's ability to prioritize deportations but deny his plan to give the illegals work permits.  Unfortunately, both Justice Kennedy and Chief Justice Roberts may be open to that sort of deal.

There is little doubt that Obama's pick for the Supreme Court, Merrick Garland, would have sided with the liberals in this case if he had been confirmed.  And the case highlights the pressing need to get a Republican elected to the White House so that Supreme Court justices can be named who respect the constitution and the limits of federal power.