Donald Trump proposed a system of religious discrimination for U.S. immigration policy on Monday, advocating a “total and complete shutdown of Muslims entering the United States,” according to a written campaign statement.

The incendiary proposal was swiftly denounced by Trump’s rivals in both parties, and as a policy proposal, it is probably illegal.

“I believe Trump’s unprecedented proposal would violate our Constitution,” said Harvard Law Professor Laurence Tribe, “both the First Amendment’s Religion Clauses and the equality dimension of the Due Process Clause of the Fifth Amendment.”

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Tribe, a constitutional law expert, said Trump’s proposal also conflicts with the Constitution’s general prohibition on religious tests outside of the immigration context. “It would also conflict with the spirit of the No Religious Test Clause of Article VI,” Tribe told MSNBC Monday evening.

Beyond the law, Tribe said it was also notable that using religious discrimination for immigration would be “impossible to administer” and “stupidly play into the hands of extreme Islamic terrorists.”

In the modern era, federal immigration law has generally cited religion to protect and welcome refugees facing religious discrimination by other countries – not to advance discrimination by the U.S. In 1980, for example, Congress passed an amendment to the Immigration and Nationality Act to protect some potential refugees facing “fear of persecution” on account of their “religion,” among other factors.

Earlier in the 20th Century, Congress did set immigration limits based on what are now considered suspect classes, such as excluding immigrants based on race or national origin. Congress repealed racial quotas in 1952, and eliminated quotas based on national origin, which had been in force since the 1920s, in 1965.

As a matter of federal law, Trump’s call to insert religious discrimination into national immigration policy would harken back to policies repealed many decades ago.

Close video CAIR: Trump's remarks on Muslims 'outrageous' Monday, CAIR Executive Director Nihad Awad called Donald Trump’s plans to “shut down” Muslims from entering the United States “appalling,” and that Trump “sounds more like a leader of a lynch mob than a great nation like ours.” Monday, CAIR Executive Director Nihad Awad called Donald Trump’s plans to “shut down” Muslims from entering the United States “appalling,” and that Trump “sounds more like a leader of a lynch mob than a great nation like ours.” share tweet email Embed

Dorf, an expert in constitutional law, noted that three years ago, the House “passed a resolution expressing regret for the Chinese Exclusion laws, which were based on ethnic prejudice,” and he told MSNBC “Immigration policy based on religious prejudice would be equally odious.”

Assessing Trump’s plan, Stanford Law professor Jenny Martinez said “Excluding all people of a particular religion from entering the country on the sole basis of their religion would, in my view, clearly violate the Constitution’s guarantee of equal protection.”

Martinez, an expert in international law, added that the only legal support for such an approach comes in older, discredited cases. “To the extent there are precedents for this kind of blanket discrimination,” she told MSNBC, “they are ones, like the Japanese internment camps upheld by the Supreme Court in Korematsu, which all reasonable constitutional experts consider tragic mistakes that we should not repeat.”