1. What, exactly, is Donald Trump proposing?
As his campaign announced in a press release issued on Monday, Trump is proposing “a total and complete shutdown of Muslims entering the United States until our country’s representatives can figure out what is going on.”
The press release did not provide any further details, but Mr. Trump subsequently clarified in an interview with ABC News on Tuesday that his ban would not apply to U.S. citizens. In his words, “If a person is a Muslim, goes overseas and comes back, they can come back. They’re a citizen. That’s different,” Trump said. “But we have to figure things out.”
Thus, it appears that Trump’s proposal is for Congress to enact a categorical bar on the admission into the country of any non-citizens — everyone from businesspeople and tourists to immigrants and refugees — who are Muslims. Even then, it is not clear — and Trump has not explained — how immigration officials would determine an immigrant’s religious affiliation other than through self-identification.
2. Is there precedent for the travel ban?
 Trump and his supporters have invoked the Japanese American internment camps from World War II as precedent for the travel ban. But that analogy breaks down for three different reasons: First, those camps were based specifically on the fact that the United States was at war with the country that the internees were either citizens or descendants of. Here, by contrast, we’re not at “war” with Islam; the armed conflict Congress has authorized is with those groups specifically responsible for the September 11 attacks — al Qaeda — and their affiliates — ISIS.
Second, the Supreme Court’s Korematsu decision, which upheld the laws that created the camps, was based on the government’s representation that it couldn’t conduct a security assessment of Japanese Americans on an individual basis. Even the Solicitor General has recently conceded that this was an intentionally misrepresentation to the Justices. Today, in contrast, the government has a vast array of authorities to screen terrorism suspects on an individual basis—including at the border.
And third, Korematsu has become one of the most reviled decisions in the Supreme Court’s history. To apply that kind of reasoning to a religious group with which we are not “at war” when the federal government has both the authority and the wherewithal to screen terrorism suspects on an individualized basis is to only compound a mistake for which the U.S. government subsequently issued an official apology.
3. Can the government really ban all immigration by a particular religious group?
In a word, no. The Constitution includes 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. Although each of these provisions serve slightly different purposes, they all reflect a basic principle—that the federal government generally may neither suppress nor support particular religious groups.
In modern constitutional doctrine, the Supreme Court has applied what’s called “strict scrutiny” to laws that discriminate among religious groups—and has therefore asked whether the law is “narrowly tailored to vindicate a compelling government interest.” Indeed, for as divided as the Justices are on any number of other contemporary constitutional topics, they are unanimous that religious discrimination is as inherently suspect (if not more so) as discrimination based upon race and national origin.
Although there will surely be widespread agreement that preventing future acts of terrorism is a compelling government interest, a categorical ban on Muslim immigration would just as surely fail the “narrowly tailored” requirement for two reasons. First, it would be both massively overbroad because an overwhelming majority of Muslim immigrants do not pose any threat of terrorism. At the same time, it would be underinclusive because not all terrorists are Muslim immigrants.
4. The government already discriminates when it comes to who’s allowed to come to the United States. Why is this different?
The Supreme Court has long recognized the federal government’s special power in immigration, and has therefore allowed Congress — albeit not Executive Branch agencies — to discriminate against non-citizens so long as it has a “rational basis” for doing so. But all of those cases involve statutes that apply equally to non-citizens of different religious affiliations and national origins—for example, statutes that impose residency requirements before non-citizens can receive government benefits.
In such cases where discrimination against immigrants has been allowed, the relevant distinction has been between recently arrived non-citizens and others, and not between Muslim immigrants and immigrants who practice other religious faiths. The Supreme Court has never suggested that Congress would receive similar deference for a statute that drew a religious distinction among immigrants—probably because, in that case, the law would offend not just constitutional anti-discrimination principles, but the First Amendment, as well.
5. Don’t foreigners generally lack constitutional rights?
It is true that, as a general proposition, non-citizens outside the United States have previously been held to have few—if any—constitutional protections. But there are two reasons to suspect that Mr. Trump’s proposed ban would still be invalidated by the courts:
First, the way the ban would have to be enforced, it would surely ensnare at least some non-citizens with prior connections to the United States. These are people who do have well-settled constitutional protections. As applied to them, the ban would clearly be unconstitutional.
Second, even as applied to non-citizens with no prior connections to the United States, the Supreme Court in recent years has suggested that at least some constitutional principles still apply. The Justices held in 2008 that terrorism suspects detained as “enemy combatants” at Guantánamo are protected by the Constitution’s Suspension Clause, which guarantees judicial review of the legality of their detention. And the Court has also suggested that the government needs an especially good reason to discriminate against undocumented immigrants who, like non-citizens outside the United States, don’t otherwise have constitutional protections.
It therefore seems likely that the courts would have no trouble holding that a categorical ban on immigration by a particular religious group violates the Constitution—even if most of the affected individuals do not themselves have constitutional rights.
