(CN) – President Donald Trump’s assertion last week that he wanted to send the New York City terror suspect to Guantanamo Bay to be held as an enemy combatant has civil liberties groups worried about the administration’s continued faith in the controversial detainment practice.

When asked Oct. 30 about the deaths of eight pedestrians by a man who allegedly acted in the name of the Islamic State group, Trump told reporters he would “certainly consider” sending the suspect, Sayfullo Saipov, to the U.S. Naval prison where past administrations had historically stored enemy combatants.

The following day, White House press secretary Sarah Huckabee Sanders clarified the White House position, saying Saipov could be considered an enemy combatant.

“I think the actions that he took certainly justify that,” Sanders said.

Though Trump walked back his earlier remarks — tweeting on Nov. 2 that it would be “appropriate” to try Saipov in New York where the murders occurred — designation of Saipov as an enemy combatant would make him the second of Trump’s term.

A power allotted to the executive branch, the enemy-combatant designation has existed since World War II and was defined by the Supreme Court’s 1942 decision known as Ex parte Quirin. The ruling created the distinction for enemy troops who come into the states “without uniform secretly … for the purpose of waging war by destruction of life or property.”

The designation allows the U.S. to hold the suspect indefinitely, without trial or access to lawyer, and eventually charge them in U.S. military courts. It can lead to other controversial practices, like “enhanced interrogation” or torture, as was seen at Gitmo.

Designations of enemy combatants returned to the spotlight after 9/11 as the U.S., under the Bush administration, worked to capture suspects and interrogate them in the pursuit of information in the war on terror.

“It matters what model of law we are aiming to uphold: American criminal law or the laws of armed conflict,” said Mike Hayden, a retired four-star general and head of the CIA after 9/11. He defended the designation and its usefulness during a 2010 debate held on NPR’s Intelligence Squared. “It’s only laws of armed conflict that will keep you safe,” Hayden said.

Despite Hayden’s support for the designation, the Bush administration had stopped the practice, at least on U.S. citizens and noncitizens captured on U.S. soil, long before 2010. The Obama administration had stopped using the designation, and began releasing Gitmo prisoners, in 2009, though the ACLU said at least 40 enemy combatants remain at the base today.

In 2001, U.S. citizen Yaser Hamdi was caught fighting against U.S. soldiers in Afghanistan. He was detained and held at Guantanamo Bay as an enemy combatant before his confinement was successfully called a violation of his Fifth Amendment rights by the Supreme Court in 2004.

“The writ of habeas corpus remains available to every individual detained within the United States,” wrote Justice Sandra Day O’Connor, a Reagan appointee, striking his confinement.

Hamdi’s case is particularly relevant to a new, “unnamed” U.S. citizen currently being detained as an enemy combatant because this person was similarly caught in an active war zone.

“An assertion that one resided in a country in which combat operations are taking place is not a concession that one was ‘captured in a zone of active combat operations in a foreign theater of war,’” O’Connor wrote.

Saipov’s immigration status as a legal permanent resident of the United States meanwhile has prompted a push by the Trump administration to roll back the Diversity Immigration Visa program that allowed him to enter the states in 2010 from Uzbekistan.

Jonathan Hafetz, a senior staff attorney with the American Civil Liberties Union, emphasized that Saipov still has protections under the U.S. Constitution.

“All individuals within the country have a constitutional right to habeas corpus,” Hafetz said in an interview. “There’s no distinction between those residing in the country and the rights of citizens.”

The ACLU has since filed a habeas corpus petition to gain access to the unnamed enemy combatant, and Saipov has been charged in New York with material support to terrorists and vehicular homicide.

Charging suspected terrorists in federal court has lead to hundreds of successful prosecutions. Meanwhile, many of those designated as enemy combatants have been released without charge or flounder in the military courts, as is the case of accused 9/11 conspirator Khalid Sheikh Mohammed who, 16 years later, is still in the pretrial phase of proceedings at Guantanamo.

“As long as the federal courts are open and we’re not under martial law, the federal courts are the sole legitimate forum to try terrorism suspects,” Hafetz said, calling the enemy-combatant program a “failure” due to the lack of successful prosecution.

A week has passed since the White House floated the possibility of designating Saipov as an enemy combatant, but Trump’s enactment of the transgender military ban and his declaration of an opioid epidemic followed similar patterns of delay.

Hafetz called such a move “completely lawless” and a throwback to “the most extreme abuses of executive detention power after 9/11.”

“To take him now and remove him from the criminal justice system would … show the [executive branch] is not serious about prosecuting terrorism suspects,” he said.

Former Gen. Hayden, during his Intelligence Squared debate, emphasized on the other hand that designation of enemy combatants is a key military power that keeps the U.S. safe. After being directly involved in a study of the effectiveness of interrogating enemy combatants, he said “making [the program] go away would have been a comfortable decision, but it would have been immoral.”

“You’ve told me, the military, to defend you,” he said. “Don’t take away the tools I need to uphold the rule of law.”