Alan Gomez

USA TODAY

MIAMI — President Obama's recent order to his administration to find ways to deport people living in the United States illegally "more humanely" has both sides of the immigration debate wondering eagerly what he means by that.

Advocates for undocumented immigrants hope it means that the Department of Homeland Security will finally decide to end all deportations, and opponents of Obama's immigration polices hope it does not.

Both sides say the law is on their side: Proponents claim Obama has every right to order a backing-away from enforcing deportation laws and opponents say he is violating his oath of office if he does.

"The Department of Homeland Security has a pretty broad range of authority to decide which individuals will be removed from the country or not," says Marielena Hincapié, executive director of the National Immigration Law Center, which advocates on behalf of legal and undocumented immigrants.

"The administration is on solid legal footing ... and can still go much further."

Ira Mehlman of the Federation for American Immigration Reform, which seeks lower levels of legal and illegal immigration, says doing so violates Obama's oath to "preserve, protect and defend" the Constitution.

"If he can simply decide, 'Congress can pass any law that it wants and I'm going to ignore the ones I don't like and create the ones I want,' then this is not just an immigration issue," Mehlman says. "This ends up becoming a constitutional issue, and it's precisely what the founding fathers sought to avert."

When the president decides, it is likely to reignite a debate going on in Congress and making its way through federal courts about the limits of presidential power that goes back decades.

At first glance, the debate seems pretty clear.

In 1954, the U.S. Supreme Court ruled in Galvan v. Press that the power to create immigration policy is "entrusted exclusively to the Congress." However, in 2002, when Congress created the Department of Homeland Security, it delegated to the department's secretary the power to establish "national immigration policies and priorities."

Obama has already alluded to that congressional mandate when establishing orders and policies for immigration enforcement.

In 2011, John Morton, then Obama's director of Immigration and Customs Enforcement, issued a memo laying out a set of principles his agents should follow when determining who to deport.

In what is known as "The Morton Memo," agents were told to focus deportation efforts on certain undocumented immigrants, such as those with extensive criminal records or those deemed threats to national security.

In 2012, the president went a step further, creating the Deferred Actions for Childhood Arrivals program. That allowed undocumented immigrants brought to the country as children to apply to the federal government to have their deportations delayed for two years. So far, more than 520,000 people have been approved.

Obama continued in 2013, granting deportation protections to the direct relatives of U.S. servicemembers and to parents with minor children.

Immigrant advocates such as Hincapié say Obama has unquestionably carried out the immigration enforcement goals approved by Congress, as evidenced by the roughly 400,000 people he deports each year. His moves to protect some segments of the undocumented population is merely his way of targeting the right people to deport, they say.

Many critics of the administration say any president has the right to exercise "prosecutorial discretion," directing federal law enforcement officers and government attorneys to focus efforts on certain types of crimes and criminals.

But Mehlman and others say a president exceeds his legal authority when he exempts broad classes of people here illegally from federal deportation laws.

That legal argument led a group of agents for the U.S. Immigration and Custom Enforcement agency, the interior enforcement arm of DHS, to sue the Obama administration. They claim the White House put them in an impossible bind because as agents they are required by law to deport people they encounter who were in the country illegally, but their superiors are telling them not to based on the principles laid out by Homeland Security leadership.

Whether that is a sound legal position has to to be decided. U.S. District Judge Reed O'Connor dismissed the lawsuit last year but only because it had been filed in the wrong jurisdiction. He said in his ruling he agreed that the agents had a strong case.

"The Court concluded that plaintiffs were likely to succeed on the merits of their claim that the Department of Homeland Security has implemented a program contrary to congressional mandate," O'Connor wrote in July.

The case is under appeal.

Some politicians who oppose Obama's exemptions of whole classes of undocumented immigrants from the law have agreed that past presidents had the right to exercise "prosecutorial discretion" in immigration cases.

In 1999, 14 Republicans signed a letter calling on the attorney general and commissioner of the Immigration and Naturalization Service to use "prosecutorial discretion" and not act on cases that had come to their attention of legal permanent residents who were deported for committing a single low-level crime years ago.

The letter-signers said prosecutorial discretion was a "well established" principle that should be used to stop the deportations they described as "unfair and resulted in unjustifiable hardship."

Signers of the letter included Rep. Lamar Smith, R-Texas, and Rep. James Sensenbrenner, R-Wis., co-sponsors of the ENFORCE Act passed by the House that would let Congress sue the executive branch for failing to enforce laws.

Smith disagreed that the letter indicates he agreed with Obama's position in the past.

"This stands in stark contrast to the president's actions that go beyond the bounds of our immigration laws by exempting broad categories of illegal immigrants from enforcement by executive fiat," he said.

The Department of Homeland Security is conducting a system-wide review of the way it enforces immigration laws per Obama's directive last week. But it is something that has been on the president's mind for a while.

"I am the head of the executive branch of government. I'm required to follow the law. And that's what we've done," Obama told Univision last year. "But what I've also said is, let's make sure that we're applying the law in a way that takes into account people's humanity."