Obama's Immigration Order Is Done. Now He Has to Make It Work.

Many questions about implementing the plan remain, as the White House enters "uncharted territory."

The work is far from over.

The White House took months to carefully craft unilateral action on immigration that it believes—despite strong criticism from the GOP—falls within the executive branch's powers. This long-awaited plan has been announced, analyzed, and commented on in a barrage of tweets, press releases, and stories. But that's just the beginning.

For the administration, it means really digging into the program's specifics, hammering out the nitty gritty of exactly of how to apply for relief.

For undocumented immigrants, it means finding evidence proving they've resided in the United States for more than five years. It means collecting years of rent receipts, utility bills, pay stubs, and more. And, for some, it means making the decision to come out of the shadows—or maybe not to, for fear the program wouldn't outlive Barack Obama's presidency.

"We're sort of in uncharted territory," said Marc Rosenblum, the deputy director of the Migration Policy Institute's U.S. Immigration Policy Program. "We haven't ever had a legalization program just quite like this, and we certainly haven't had a legalization program like this that's been overturned by a future president."

The executive order announced Thursday night lets undocumented parents of U.S. citizens or lawful permanent residents apply for a three-year temporary deportation deferral and work permit. But there's another hook: They must have lived in the United States for more than five years, and they have to prove it.

This isn't a new concept. Beneficiaries of a previous program established by an executive order, called Deferred Action for Childhood Arrivals or DACA, had to do the same. But these were children who had arrived in the United States before their 16th birthday, and oftentimes school records could be easily obtained, Rosenblum said. Proving residency could be more challenging for adults.

"If you've been working off the books and maybe living in an informal situation, it may be hard to document continuous presence," Rosenblum said.

The burden of proof is on the applicant, according to Michael Jarecki, treasurer of the American Immigration Lawyers Association's Chicago chapter. Proving residency often hinges on a collection of medical bills; taxes; affidavits from religious and civic organizations; and more.

But it can be challenging for one big reason. "They might not have clear information," said Jarecki, who practices U.S. immigration and nationality law in Chicago. "In fact, those people may have purposely not wanted to sign things and say that they were here in this country because they knew they were here undocumented."

Then, there's the meaning of the word "parent."

The Immigration and Nationality Act considers it someone who is a parent of a child born in wedlock, a stepchild, or adopted under certain criteria. It also includes mothers using assisted reproductive technology even if they're not the genetic parent.

"How do you define a parent in particular is probably a policy question they haven't decided on yet," Rosenblum said, "or they certainly haven't published an answer to yet."

As the application criteria are ironed out, there's another question that looms perhaps even larger, surrounding the number of people who will take advantage of the program. And there's a litany of reasons why undocumented residents might be cautious.

First, they want to ensure it's not a witch hunt, Jarecki said. It could be a wait-and-see reaction similar to DACA, where some undocumented immigrants watched as their family, friends, and neighbors were accepted to the program without repercussions. Then, they decided to apply.

Those who have a stable job and aren't looking for a new one might decide it's safer to keep their names off the government's books, Rosenblum said.

And a level of uncertainty remains with the lame-duck session not yet over and a Republican majority set to take the helm when a new Congress convenes. On Friday, House Speaker John Boehner reiterated his commitment to fighting the president's executive order, making it clear Obama's unilateral action had significantly decreased the chances of comprehensive immigration legislation passing both chambers.

"If this program remains hotly contested," Rosenblum said, "and Republicans attack it, that may contribute to unauthorized immigrants being more reluctant to take advantage of it."