President Obama is reportedly mulling an executive action that could defer deportations for as many as five million illegal immigrants, for example by broadening the program for people brought here illegally as children to include their parents and the parents of children who are already U.S. citizens. It’s still unclear what he will do — he could still pursue options that are considerably less ambitious — but Republicans are already gearing up to paint his move as the latest act of an imperial president bent on circumventing Congress when it won’t give him his way.

John Sandweg was acting general counsel at the Department of Homeland Security from 2012-2013, during the establishment of Obama’s Deferred Action for Childhood Arrivals program. He was also acting director of Immigration and Customs Enforcement from late 2013 until early this year, when he stepped down amid GOP criticism. He is among those who is most knowledgeable on the topic.

I asked him to detail what he sees as the legal justification for DACA and any potential expansion of it, and pressed him to respond to conservative criticism. An edited and condensed version of our conversation follows:

1) It seems to me the key distinction here is that it’s fine to exercise prosecutorial discretion on a case by case basis, but once you cross over into exempting whole classes from prosecution, you risk straying into policy-making and law-rewriting.

SANDWEG: The president is doing what every single law enforcement agency across the country does: Put in place rational priorities to ensure that limited resources are focused on the populations that pose the greatest threat to public safety and border security. Every single law enforcement agency in America struggles with the fact that their resources are not conditioned to cover every single violation of the law. What prosecutors and police chiefs have done for years is implement enforcement priorities. That’s what the president has done.

2) Why does exempting whole classes not constitute failure to enforce the law?

SANDWEG: There are very limited resources in the enforcement system. There are 11.5 million people in this country who are already technically in violation of immigration law. In 2012 ICE removed approximately 400,000 individuals — the highest total in the government’s history of removals. Approximately 200,000 of them were arrested in the interior. That is less than two percent of the undocumented population. This shows how limited the resources are and shows you have to make decisions. This isn’t a zero sum game.

ICE officers have always exercised discretion, and always implemented priorities in terms of picking and choosing which types of cases to move to the front of the line over others — prioritizing the removal of convicted criminals, or those just apprehended crossing the borders, above others. If you choose to expend resources on those who have been here 15 years and have never committed a criminal offense, that means somebody who has committed a felony is more likely to be able to stay in the U.S.

3) Is the argument that prioritizing one group over another for removal is inevitably, and already, the way business is done? Is the argument that the president is merely clarifying something that would already be happening?

SANDWEG: This has always been how the system has operated. There is inconsistency when there is a lack of uniform guidance. You have 24 field offices and roughly 6,000 ICE immigration enforcement agents across the country, all of them exercising priorities. But absent some uniform guidance, it can be done inconsistently. What the President has done is provide clarity and guidelines about how best to utilize that discretion to ensure consistency across the country in a manner that will ensure a consistent focus on criminal aliens and recent border crossers.

4) What would happen if Republicans got their way and Obama did not deprioritize the removal of DACA beneficiaries or parents of DACA beneficiaries or U.S. citizens?

SANDWEG: There are only so many people ICE can remove from the United States. The question is, how do you choose which of the 11.5 million you are going to remove? If you begin by eliminating DACA and eliminating prosecutorial discretion policies, what you’d be doing is increasing the likelihood that the people removed are those who pose no threat to public safety. You’d be making it more likely that convicted criminals and people who just crossed the border are going to remain in this country. You’d be making the country less safe. If we eliminated all priorities, and treat them all equally, you are going to make the country less safe, and make the border less secure.

5) But why can’t they just circulate an internal memo laying out priorities, the way they did with the Morton Memo? Doesn’t it cross a line into rewriting the law when you publicly announce that a whole class is temporarily not going to be subjected to enforcement? Doesn’t that constitute awarding affirmative status?

SANDWEG: It’s the role of the leadership to provide guidance to the field about how best to enforce the law. Whether the memos or policy documents or guidance are made public or not is irrelevant to the central question. In my experience everything goes public. There is nothing that stays internal. There are reasons to make issues like this public and to raise awareness and clarification to law enforcement partners to ensure that the field is fully aware of the guidance of the agency.

DACA is a law enforcement tool that is the logical next step from the Morton Memo. DACA provides additional clarity and guidance to the field. But it doesn’t guarantee a class of individuals anything. It does not provide or confer any rights upon individuals. What it does is provide guidance that officers and agents are to consider when determining how to exercise discretion. It requires an individual case by case analysis of whether those factors apply in any particular case. It does not confer upon any class any rights.

6) Would this apply to an expansion of DACA?

SANDWEG: Yes. Obviously it depends on how it’s constructed, but Yes. It would be adding additional or different criteria to consider. (See Note 1 below.)

7) What about offering them work authorization? Doesn’t that go beyond just deprioritizing removals? Conservatives would point out that even if you can justify executive discretion deferring deportations, offering work authorization crosses into rewriting of the law.

SANDWEG: Longstanding law already allows for individuals who are granted deferred action to gain work authorization. This is not central to how and why a policy like DACA makes sense. We were looking for a tool to help our officers and agents to better do their jobs. The easiest way to effectuate that was granting deferred action. There was a longstanding, preexisting regulation that governs who gets work authorization; deferred action recipients were included in that regulation — a decision that was made long before this administration. (See Note 2 below.)

8) Don’t critics have a point when they say that even if these programs are temporary, in effect it’s probably permanent relief from deportation, because they will be renewed?

SANDWEG: By law these programs are subject to the discretion of the president. Future presidents are certainly free to change them. DACA could be recinded by a future president. The president has made it very clear that these are no substitutes for Congressional action. Acts of discretion are not permanent.

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NOTES: I asked attorney David Leopold, former president of the American Immigration Lawyers Association and immigration reform advocate who has consulted with the White House on immigration law, to expand on a couple of the points above.

1) On Sandweg’s answer to Questions 5 and 6, Leopold adds:

The key difference between the Morton Memo and DACA is that the latter is more specific. DACA applicants must file a form, but the grant of DACA confers no lawful immigration status. While it is true that DACA applies to categories, it does not cross over into anything even remotely equivalent to granting any category any kind of new protection under rewritten law, because it does not create any new right or legal immigration status. The government retains its authority to unilaterally revoke DACA, either categorically or individually, at any time and for any reason, subjecting an undocumented immigrant to removal.

It is true that there is no bright line test delineating the parameters of the President’s authority to grant Deferred Action. Perhaps one way to think about this is to ask whether the exercise of prosecutorial discretion in question — whether categorical or not — can reasonably be seen as legitimate prioritization of limited law enforcement resources. If so, it arguably falls well within President’s legal authority. This would include individual as well as categorical grants of deferred action, such as DACA. As the Supreme Court recognized in Arizona vs. U.S., some “discretionary decisions involve policy choices.”

2) On Sandweg’s answer to Question 7, Leopold adds:

Though many argue that DACA grants its beneficiaries work status, in fact, the regulation that grants work status to undocumented immigrants who have been granted deferred action predates DACA and applies to many other categories of people granted deferred action. The federal regulations governing employment under immigration law existed well before DACA. Under those regulations, any undocumented immigrant granted deferred action — under programs that preceded DACA or coincide with it — had already been able to apply for employment authorization. It requires them to demonstrate economic necessity. That applied to anyone granted deferred action either individually or categorically.

Therefore, DACA did not create this authorization to work — and nor would its expansion. It simply created a new category extending an already existing work authorization for beneficiaries of deferred action. The president’s authority to grant work status long precedes DACA, and while it does apply to DACA and would apply to its expansion, it is not a direct outgrowth or creation of either.

Greg Sargent writes The Plum Line blog, a reported opinion blog with a liberal slant -- what you might call “opinionated reporting” from the left.