With Obama administration officials debating how aggressively to use unilateral action to shield people from deportations, more than 100 immigration law professors have signed a letter to the President arguing that he has expansive legal authority to act to temporarily protect additional groups from removal — and that this authority is rooted in statute, court opinion, regulations, and precedent.

The letter, which was shared with this blog before its release, is designed to make the case to media and opinion-makers that Obama has maximum legal room to maneuver — which could shape how much political space the administration thinks it has on this difficult and explosive decision.

The letter — which was distributed by the American Immigration Council and the National Immigration Law Center — was signed by over 130 professors, attorneys and experts, some from the major Ivy League law schools, and others from border and red states that are relevant to the politics of this decision.

All indications are that the president may move to expand Deferred Action for Childhood Arrivals — which shields hundreds of thousands of undocumented immigrants from deportation — to other groups, such as their parents and parents of U.S. Citizens. That could amount to millions of people.

The short version of the letter’s argument is as follows. The administration has the authority to exercise “prosecutorial discretion” when deciding how to apply limited resources to the act of enforcing immigration laws. This discretion is grounded in the Constitution and has been recognized in statute and regulations for decades. Numerous administrations have used prosecutorial discretion to protect both individuals and groups from removal — and have historically justified these actions with humanitarian reasons.

The argument continues as follows. There are multiple forms of prosecutorial discretion, of which “deferred action” is one. Deferred action, too, has existed as a category for many years — and predates DACA. Therefore, DACA  and/or its expansion confer an already existing designation and create no new form of immigration status. While deferred action does confer the ability to work, it did so before DACA. Deferred action — before, and under DACA and/or its expansion — merely provides a temporary reprieve from deportation, without providing any route to permanent residency or formal legal status. What’s more, before DACA, previous administrations, and the Obama administration, granted deferred action not just to individuals, but to large classes as well.

In other words, the letter seeks to rebut the leading legal and political arguments against both DACA and its expansion — the suggestion that granting deferred action status to groups crosses a line into rewriting or non-enforcement of the law; and the notion that it confers a quasi-amnesty status. Some have argued that the scale and numbers of those impacted by DACA and/or its expansion, combined with the awarding of work authorization and bureaucratic trappings, push the program into new territory. But the letter concludes:

Some have suggested that the size of the group who may “benefit” from an act of prosecutorial discretion is relevant to its legality. We are unaware of any legal authority for such an assumption…A serious legal question would arise if the administration were to halt all immigration enforcement, because in such a case the justification of resource limitations would not apply. But the Obama administration to date appears to have enforced the immigration law significantly through apprehensions, investigations, detentions and over two million removals.

In conclusion, we believe the administration has the legal authority to use prosecutorial discretion as a tool for managing resources and protecting individuals contributing to the United States in meaningful ways. Likewise, when prosecutorial discretion is exercised, there is no legal barrier to formalizing that policy decision through sound procedures that include a form application and dissemination of the relevant criteria to the officers charged with implementing the program and to the public. As the Deferred Action for Childhood Arrivals (DACA) program has shown, these kinds of procedures help officers to implement policy decisions fairly and consistently, and they offer the public the transparency that government priority decisions require in a democracy.

That last point has implications for the political debate as well as the legal one. Some have argued that even if an expansion of DACA is legal, it violates political norms because it seems to flout Congress by crossing over into policy-making territory. But the counter-argument here is that DACA amounts to the streamlining, clarification, formulation, and implementation of broad enforcement priorities that pretty much everyone already agrees are legitimately within the executive’s authority to apply. So the question for those making the political norms argument is: If it’s legitimate to exercise prosecutorial discretion in this fashion, why isn’t it also legitimate to refine its implementation in ways designed to benefit the country?

The problem, as I’ve noted before, is that the question of whether something like this violates “political norms” is largely subjective. This does feel like something new. Leading opinion-makers have already demonstrated ample discomfort with it, based (again) on what appear to be largely subjective grounds. Partly because of this — and partly because of other political and demographic considerations — vulnerable Democratic incumbents and Dem operatives don’t want to take on this political challenge before the elections. There’s a good case to be made that such worries are overstated and that delaying may not solve the political problems that will inevitably be associated with these actions. But Dem worries appear to run very deep and may lead Obama to delay. For all we know the administration itself may decide it is far more constrained from acting than many lawyers and experts believe.

In this context, the letter can also be seen as an effort to stiffen the spines of Democrats who worry about the politics of Obama’s coming action and of administration officials who may be inclined towards a cramped view of his legal authority to move forward with it.

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