That program, labeled the National Security Entry-Exit Registration System, required those entering the U.S. from a list of certain countries — all but one predominantly Muslim — to register when they arrived in the U.S., undergo more thorough interrogation and be fingerprinted. The system, referred to by the acronym NSEERS, was criticized by civil rights groups for targeting a religious group and was phased out in 2011 because it was found to be redundant with other immigration systems.

Robert McCaw, director of government affairs for the Council on American-Islamic Relations, said a reinstitution of NSEERS would be akin to “just turning back the clock.” CAIR will lobby heavily against the system as not only discriminatory but also ineffective, McCaw said, if it ends up being proposed by the Trump administration.

He also accused Kobach, an architect of the original NSEERS program when he was with the Justice Department under the George W. Bush administration, of having “a long ax to grind with the Muslim community.”

“NSEERS and registries like it are totally ineffective and burdensome and they’re perceived by Muslims and other minorities as just being a massive profiling campaign that, in the past, targeted Muslim travelers solely based on their religion and ethnicity,” he said. “When every country on that list happens to be a majority-Muslim country, it is religious profiling. Because there are threats from other nations and other communities and groups that don’t make it on NSEERS.”

The ACLU said a resurrection of the NSEERS program would be illegal and slammed it as ineffective and “harmful to our national security.”

“President-elect Trump and his immigration advisers have taken an illegal and long-ago abandoned post-9/11 program, the National Security Entry-Exit System, and now threaten to reignite it,” the ACLU’s Immigrants’ Rights Project director Cecillia Wang said in a statement. “Let’s be clear: Trump is talking about a federal dragnet that targets people for registration, surveillance, interrogation, or detention because of their religion. Such a dragnet would be unconstitutional.”

But a program like NSEERS would likely pass constitutional muster before a judge, multiple experts said, in part because it already has. The system was never struck down by a court in the nearly nine years it was in place.

Jonathan Turley, a law professor at George Washington University, said Wednesday that “a president’s power is at its apex at the nation’s borders” and that the Supreme Court has “consistently reaffirmed the power of the president to control the entry and exit from the country as a matter of national security.” Such precedent, he said would give Trump’s administration a decided advantage in any litigation.

Immigration law would afford the government special advantages, Temple University international law professor Peter Spiro said, because it exists in a “parallel universe” where many of the constitutional protections afforded in other legal situations do not apply. He said “discrimination on the basis of nationality is something that, again, one finds all over the immigration law, and in a nonimmigration context would almost certainly not withstand the equal-protection challenges.”

Despite its ability to pass constitutional muster, Spiro is no fan of the NSEERS, which he called “a terrible policy” and “a silly program in a lot of ways.” He said the program failed to catch terrorists and created some “pretty tragic cases” in which immigrants already in the country registered under the system and wound up being deported because their immigration status had lapsed.

“You can’t say it’s not discriminatory. It’s only, you know, nationals of certain countries and they’re predominantly Muslim ones,” Spiro said. “It’s terrible policy, zero counterterrorism value, and yet, in this parallel universe, you know, constitutional universe that applies to immigration law, pretty constitutional.”

“It’s immigration security theater,” Spiro added. “It’s like the wall: It’s pretty clear that it just has no effect, but it’s a way of keeping the restrictions constituencies, or the alarmist counterterrorism constituency, happy.”

Even Trump’s original proposal to bar all Muslims from entering the country could potentially end up passing a constitutional test, Spiro said, telling POLITICO that “my guess is that a court would strike that down, but it’s not clear, actually.” That Trump has backed away from that position, taken during the GOP primary, and assumed the more legally defensible “extreme vetting” one, is evidence, Spiro said, that he was given legal advice on the issue. “Kris Kobach knows his stuff. And I assume it was Kobach or somebody else [who] got to Trump and Trump was changing his tune,” he said.

Like Spiro, University of Virginia international law professor emeritus David Martin said the NSEERS program is constitutionally sound but fraught with issues as a matter of policy. He said even when it was in effect, NSEERS was “more and more seen as potentially counterproductive” as the Sept. 11 attacks receded in America’s rear-view mirror and the government developed “more of an appreciation that doing certain things that singled out Muslims and were seen as discriminatory were strategically unsound.”

Martin, who was also the general counsel for the Immigration and Naturalization Service from 1995-8 and a principle deputy general counsel at the Department of Homeland Security early in the administration of President Barack Obama, said reconstructing an NSEERS-like system would be a “really bad idea, for a lot of reasons, absent some extreme danger to the country far beyond anything we face now.” But he added that such a program would be “not likely to meet with successful constitutional challenge.”

Still, he said, the cries of discrimination that have already begun from organizations like CAIR and others carry tremendous moral and political weight.

“It’s kind of an American tradition to claim that things you disagree with are unconstitutional, and sometimes are out of keeping with the spirit of constitutional values, even if ultimately a court might uphold them,” Martin said. “So, I think it’s quite legitimate to argue on the basis of constitutional values even if you don’t absolutely have a Supreme Court precedent that clearly establishes your point.”