MADISON, Wis. (AP) — Donald Trump's call to block all Muslims from entering the United States is not only unconstitutional, but also impossible to carry out, legal experts said Tuesday.
Trump's proposed ban, announced to cheers at a rally in South Carolina Monday, would apply to immigrants and visitors alike, a sweeping prohibition affecting all adherents of a religion practiced by more than a billion people worldwide.
Beyond inciting condemnation from Republican presidential rivals, GOP leaders and others, legal and immigration experts said Tuesday that Trump's proposal violated the Constitution's equal protection clause and freedom of religion granted under the First Amendment.
"It is blatantly unconstitutional and it's an attack on the very foundation of the United States," said Marci Hamilton, a law professor specializing in the First Amendment at Yeshiva University in New York City. She called his idea "laughable."
"It's never possible to fully ascertain what someone believes internally," Hamilton added. "How does one recognize a Muslim, a Christian or a Jew? Do you look at where they were born, do you look at where they were raised? Do you look at the last religious service they attended?"
Trump's proposal amounts to a religious test for anyone wanting to enter the country, something that is unprecedented in U.S. history, said Nancy Morawetz, a professor of Clinical Law at the New York University School of Law.
"If one has this kind of a rule, you have to figure out how you're going to test it and verify it," Morawetz said. "What this really means is there would be a religious identity card."
Even an anti-immigration group that for decades has advocated curtailing the influx of immigrants to the U.S. disavowed Trump's religion-based exclusion.
"Nobody's interested in selecting people solely on their religion or their faith," said Dan Stein, president of the Washington-based Federation for American Immigration Reform.
Trump's comments highlight the broader concern over the immigrant vetting process, Stein said.
"Donald Trump is unartful, but it seems to us what he's really putting his finger on is this broader question of suspending a significant swath of immigration until this country can reassert a better screening process," Stein said.
U.S. immigration law has some "very, very ugly history" where people have been turned away based on their nation of origin, but never on their religion, Morawetz said.
In the late 1800s, Congress passed legislation broadly aimed at halting the immigration of Chinese laborers. Those were not fully repealed until 1943. Quotas limiting immigration based on race and national origin were also enacted in the early 1900s. Racial quotas were repealed in 1952, and those limiting people based on national origin were eliminated in 1965.
Legal scholars believe such bans, if proposed today, would not be found to be constitutional, Morawetz said.
Religion can factor into immigration decisions, but that typically happens when people are fleeing religious persecution. So people of a particular religion may get favorable treatment by the United States, as when Russian Jews sought to leave the Soviet Union.
Trump, who has built his Republican presidential candidacy around inflammatory rhetoric, stood by his latest statements Tuesday, saying stopping all Muslims from entering the U.S. is necessary because of hatred among "large segments of the Muslim population" toward Americans.
Trump said banning all Muslims "until our country's representatives can figure out what the hell is going on" is warranted after attacks by Muslim extremists in Paris and last week's shooting in San Bernardino, California, that killed 14.