Republican presidential candidate Donald Trump's controversial idea for a a "total and complete" shutdown of Muslims entering the United States until "our country’s representatives can figure out what is going on" has elicited a ton of response.

Alongside denigration from some Jewish and Muslim leaders, the rest of the GOP and Democratic presidential field and the White House, there have been calls to have him banned from the UK and, on Wednesday (Dec. 9) a bow of support from News Corp. (Fox News) boss Rupert Murdoch.

But one question hung over the entire affair: is what Trump's proposing even legal? As it stood after his first suggestion of the policy on Monday night, CNN reported that the basics of Trump's plan would not likely hold up to legal scrutiny.

After some contentious interviews on Tuesday morning in which he refused to back down on his comments, Trump clarified his stance while talking to ABC News, explaining that his ban would not apply to U.S. citizens of Muslim descent. "If a person is a Muslim, goes overseas and comes back, they can come back," he said. "They're a citizen. That's different. But we have to figure things out."

Some have compared the plan to the program of Japanese internment during WWII, in which more than 100,000 Japanese -- most of them American citizens -- from the West Coast were forcibly moved into camps during the war. Trump has denied that he is after that kind of action.

"This is a president highly respected by all, he did the same thing," Trump said of late president Franklin Delano Roosevelt. "If you look at what he was doing, it was far worse. I mean, he was talking about the Germans because we're at war... We are now at war. We have a president that doesn't want to say that, but we are now at war."

Is It Even Legal?

While Trump's plan is still not totally clear, CNN reported that he appeared to be proposing the barring of admission into the country of any non-citizen Muslims, from businesspeople and tourists to immigrants and refugees, though it's also not clear how immigration officials would "determine an immigrant's religious affiliation other than through self-identification."

While CNN noted that Trump and his supporters have used the Japanese camps as a precedent for the ban, that analogy falls apart in the network's eyes for several reasons: the Japanese camps were specifically tied to a war with a nation "that the internees were either citizens or descendants of" and we are not at "war" with Islam, but with terror group such as Al Qaeda and ISIS. Also, today we have a variety of ways to screen terrorism suspects on an individual basis (unlike back then, when the government claimed it couldn't conduct a security assessment of individual Japanese Americans).

CNN also noted that the U.S. Constitution has "four different clauses limiting the federal government's power to discriminate on the basis of religion—the Free Exercise and Establishment Clauses of the First Amendment, the Due Process Clause of the Fifth Amendment, and the Religious Test Clause of Article VI." Plus, the Supreme Court would be likely to view any such policy as "massively overboard because an overwhelming majority of Muslim immigrants do not pose any threat of terrorism" and "underinclusive because not all terrorists are Muslim immigrants."

Maybe It Is, Though

A number of legal scholars told the New York Times that the proposed policy of "excluding all foreign Muslims" from visiting the U.S. would be "ludicrously discriminatory and overwrought," but it's not a slam-dunk that the Supreme Court would block such an action.

The paper explained that under a provision of the existing immigration law, Congress has given the president "broad power to issue a proclamation indefinitely blocking 'the entry of any class of aliens into the United States' that he or she thinks would be 'detrimental to the interests of the United States.'" Now, no president has ever used that power in a broad way, but experts said it offers some wiggle room for a President Trump to execute his plan.

If he did though, anyone affected by the policy already in the U.S. -- including someone trying to reunite with a family member or a university that was seeking a guest lecturer -- could file a lawsuit. There are some other issues, including an international treaty that the U.S. has ratified, the International Covenant on Civil and Political Rights, which bars discrimination against people based on their religion.

Any lawsuit trying to use that provision would have to go up against Congress, which has not made it enforceable in domestic courts and the Supreme Court is unlikely to "decide that the treaty provided the judiciary with authority to strike the policy down." In fact, for most of the country's history, the Court has usually deferred to Congress and the Executive branch when it comes to issues of foreign policy, according to the Times.