As he prepares to make his fifth trip to argue before the U.S. Supreme Court in perhaps his most high-profile case to date, Texas Solicitor General Scott Keller is confident he and his team will prevail and stop President Obama's immigration plan from taking effect.

The nation's high court will likely take up Texas v. United States in April. The arguments will focus on Obama's controversial executive order, known as Deferred Action for Parents of Americans and Lawful Permanent Residents, or DAPA, which would shield more than 4 million undocumented immigrants in the country from deportation proceedings and allow them to apply for a three-year work permit. Lower courts have already ruled to halt the policy three separate times.

Keller and Chip Roy, the first assistant attorney general, sat down with The Texas Tribune recently to explain why the case isn't as simple as some think, what the state is actually fighting for and why, contrary to what some immigrant rights groups say, what Obama did isn't that same as actions taken by his predecessors.

The attorneys also discussed how the office operates while their boss, Texas Attorney General Ken Paxton, faces criminal chargesin state district court.

The following is an edited and condensed transcript of the interview.

The Texas Tribune: Several presidents have taken executive actions on immigration. Why is what President Obama did illegal and why do you think the Supreme Court is going to side with the state of Texas?

Keller: The fact that the president has taken some executive action on immigration, that’s not why the lawsuit was filed.  The same day that the memo that we’re challenging was filed, there were nine other immigration executive memos. We’re not challenging any of those nine. The memo that we’re challenging goes far beyond deportation. What it does is it grants lawful presence to millions that are here, who are here, unlawfully. And what that means is that there is going to be benefits and eligibility for benefits that come with that, such as Medicare, Social Security, the earned income tax credits, unemployment insurance, driver’s licenses. In addition to that, work permits.  So it’s that affirmative act of granting lawful presence status and eligibility for benefits that violates the law and that’s why it’s unlawful.

“The thing we always have to clarify is that this is not an immigration question – this really is a separation of powers question: What does the president have the power to do?”— Texas First Assistant Attorney General Chip Roy

TT: So this (lawsuit) is in opposition to the benefits and not against the prosecutorial discretion aspect of choosing which immigration cases not to pursue?

Keller: Our lawsuit doesn’t impact the executive’s ability to exercise prosecutorial discretion. Our injunction doesn’t require the executive to remove anyone, it doesn’t require it not to remove anyone, and it doesn’t interfere with removal priorities. What it’s about is the affirmative granting of lawful presence and lawful eligibility.

TT: Brownsville-based District Court Judge Andrew Hanen first ruled in February that the president violated the federal Administrative Procedure Act when he announced DAPA. That seems like a technicality about a posting requirement. Is it?

Keller: What he did say is the administration needed to go through notice and comment procedures. But I wouldn’t characterize this as a technicality. This is a key feature of what Congress has said. If we’re going to have administrative agencies and we are going to give them and delegate to them power, this is the key mechanism through which there is Democratic participation when administrative agencies take action. So this is not simply a “They didn’t put a piece of paper up on a courthouse door.” They would have received thousands of comments, some of them may very well have caused them to change the actions they were taking, especially given everything that’s come out in this lawsuit. 

Now the Fifth Circuit Court said not only was this a procedural violation but it was also substantively unlawful and we’re continuing to press those arguments at the Supreme Court.

TT: When he filed the lawsuit, Gov. Greg Abbott also said, "Look, we have proof this is going to harm Texas based on the unaccompanied immigrant minors that came to Texas in 2014." Can you walk me through that analogy?

Keller: We have four different arguments for standing (in that Texas has proven that it is a party that’s being directly harmed by Obama's action). The basis on which both the district court and the Fifth Circuit have said we absolutely have standing on are costs to our driver’s license program. This memo would mean hundreds of thousands of additional unauthorized aliens would become eligible for driver’s licenses and that would impose significant costs on the state of Texas. Another aspect for which we have standing on are costs from education and health care and law enforcement that are caused by additional unauthorized aliens being in the country

And the federal government’s conceded that a policy by which you are going to grant lawful presence and all these benefits will mean there are going to be additional unauthorized aliens in the country and in the state that otherwise wouldn’t stay in the state. So what that means is the state of Texas is going to be spending tens of millions of dollars.

TT: Isn’t the education issue already settled? Isn’t it long-standing policy that if you’re here and you show up to a public school, you have to be given an education?

Keller: Precisely. What that means though is the federal government, as the Supreme Court has interpreted the Constitution, says that states have to spend that money. What this memoranda is doing is it is giving lawful presence and benefits which means - it is not only likely -  but it will cause additional unauthorized aliens to remain in the country and therefore to avail themselves of those services that we are required to perform.

TT: If the (Obama administration's) ... directives to focus on what the government calls the "worst of the worst" have been in place since 2008, why are you all making the assumption that these people that are now going to cost the state money would have left had in not been for this (executive action)? 

Keller: Well the district court made that fact finding, so it’s not even just an “assumption.” But second of all, even the federal government has said that this policy obviously has wide impact on the states and the states are going to bear many of the costs of this program. In 2012, the U.S. Supreme Court, in a case called Arizona v. The United States, explicitly recognized that the states have a vast interest in immigration policy and that the states are going to bear the brunt of immigration policy.

TT: What can states do as far as state-based immigration?

Keller: Well in a case called Chamber of Commerce V. Whiting, which was based on employers, states can obviously regulate employers to a degree. There are going to be issues about when federal law preempts state law in an immigration context and we completely acknowledge that. But when we're talking about the president’s memorandum to grant 4 million unauthorized aliens lawful presence and ineligibility to benefits the issue here is not about preemption, it's about the separation of powers. When you say “The federal government has wide authority on immigration,” – that’s right. But the Constitution gives that (authority) to Congress.

TT: Would this lawsuit have been filed if it didn’t affect so many people, more than 5 million? At least in the court of public opinion, do you think that had a lot to do with it?

Keller: Obviously the lawsuit was filed  under then-Attorney General Abbott, so I won’t speculate as to the motives. But to go back to your question that every president has done something like this, I don’t think that’s accurate. There is a difference between using discretion to not deport certain people and past presidents have certainly used that discretion. But that’s different than taking the additional steps and saying we’re not going to deport certain people but then we are going to declare them lawfully here and give them benefits.

Typically (as) a use of enforcement discretion, the government is going to say, "We are not going to process this through the system." For instance, in Colorado where they are not going to process you for low-level marijuana crimes. No one thinks that what the government is doing is saying “You are actually in lawful possession of that low level of marijuana.” But yet here what this (immigration) memo is doing is saying you are lawfully present in the country even though Congress has said it’s unlawful.

Chip Roy: Keller and I both worked for Senator (Ted) Cruz, (a former Solicitor General) and lived through the immigration debates in 2013. Prior to that I was there with Sen. (John) Cornyn, (a former Texas Attorney General), in 2006 and 2007. I bring that up to say that it’s not like this issue has not been debated roundly and heavily. I think that’s relevant here because it goes to the point about what this president is doing. And in light of the fact that this has been debated and in light of the fact that there has been no conclusion reached, the president then unilaterally takes a position that would affect 4 to 5 million people with the stroke of a pen. I don’t know if there’s some magic number – 200,000 or a million or 4 million - but the nature of what the president is doing here matters a lot in the context of the extraordinary debate that we saw on Capitol Hill. Having lived through it, I can tell you that the amount of interaction we had with the American people, that matters and that goes to the heart of this issue. When the American people are engaged, they have real concerns about this policy.

TT: Why was the lawsuit filed in Brownsville? There have been a lot of people who have said that Abbott went shopping for a judge who has been on record about how frustrated he is about the illegal immigration situation. Was that a factor? 

Roy: To echo what Scott said, we weren’t here in December. It was the previous administration that made that determination. But I’ll just mention that out of the thousands of cases we deal with, rarely when we’re dealing with lawsuits out in Travis County or filed throughout the state in venues that may or may not be favorable, we don’t often get a lot of venue questions about that. But specifically on this, it’s South Texas. It’s not like this was filed in a jurisdiction that has no connection to the issue at hand. This is in the heart of the area where you’re going to feel the real impact. And there was no guarantee they were going to get Hanen.

TT: Have any recent decisions by the U.S. Supreme Court, either on marriage equality or Obamacare or anything else, affected your strategy on immigration?

Keller: I think the justices take seriously every single case that goes before them. And when they see this case they are going to see an executive that is pushing through a sweeping theory of executive power. And the court takes the separation of powers very seriously and forcing the separation of power is something the court has done for decades.

Roy: I think we don’t get in the prediction business. I know these sound like talking points but it’s actually meaningful that we’ve won three times. The arguments are very strong. The thing we always have to clarify is that this is not an immigration question – this really is a separation of powers question: What does the president have the power to do?It’s actually breathtaking from our perspective the impact that this can have on the power of the executive going forward if it’s not properly checked.

And to be clear it’s certainly not a partisan issue. It does not matter who is in The White House. One of Scott’s predecessors, Sen. Ted Cruz, argued Medllín (v. Texas case). And that was directly against the Bush administration. There are times when it's important to directly stand up for this core balance of power that’s so critical.

TT: If I may change gears a bit and ask about something else. Attorney General (Ken Paxton) is obviously going through some issues that have been made very public. How is the office functioning since the indictments were handed down? Do you guys communicate a lot with him? Is the issue not mentioned in the office?

Roy: This agency is over 4,000 people of committed public servants, most of whom have predated us and many of who will probably be here after us.  We have 700 and something lawyers, 29,000 cases, we collect $4 billion in child support. It is more than a full-time job for all of us.

We’re in constant communication with the attorney general and we’re focused on doing our job every day to defend the state of Texas. I know that that sounds like some playbook or a talking point. But it’s true.

TT: Have you shouldered more of a leadership role though? I know there are thousands of employees here but you two are probably a lot closer to the attorney general than 3,998.

Roy: The first assistant attorney general, the solicitor general, our head of civil litigation, all of us are charged to manage the daily affairs of this agency and that’s what we’re doing. I don’t know what to compare it to – I didn’t serve in a previous administration. What I know is that the attorney general hired us to do a job and that’s the job that we’re doing.