Below is my column in the Washington Post on Donald Trump’s proposal of “extreme vetting” for immigrants to the United States. While some have suggested that the proposal would violate the Constitution, I do not agree. There are ample concerns or objections that can be raised as a matter of policy. However, such vetting is neither unconstitutional nor unprecedented. Particularly if implemented with congressional approval, I believe that such a heightened level of scrutiny would pass constitutional muster. Conversely, this is clearly something that Congress could prevent legislatively.

Donald Trump’s newly proposed ideological test for immigrants — one that he characterized as “extreme vetting” in a speech on Monday — has renewed debate over immigration reform in the presidential election.

It’s a debate worth having, and there are plenty of valid questions to be raised about his proposal. This is one occasion, however, when Trump may have the law on his side. As a general proposition, a litmus test for new immigrants isn’t unconstitutional or even unprecedented. Indeed, Trump could cite an unlikely figure in support of the authority for such changes: President Obama.

Trump wants to screen potential immigrants for “hostile attitudes towards our country or its principles” and ban those who harbor those views; or who, in his words, believe that sharia law should “supplant” our system of laws; or those who express “bigotry and hatred” with regard to gender equality or gay rights. Although Congress could block these conditions, Trump would have considerable leeway in requiring background checks and imposing such tests. It has happened before: During the Cold War, there was ideological screening under the 1940 Alien Registration Act, designed to prevent the entry of communists, anarchists and others. Immigrants are currently required to know basic civics as part of a citizenship test, and Trump’s extreme vetting would require visa applicants’ affirmative agreement with those principles — though he wasn’t clear whether he would do this with a legislative change (which would be unassailable) or a unilateral executive action.

One can question how successful a litmus test would be — after all, applicants could simply lie, and such a test would just encourage potential immigrants to refrain from expressing their views on social media or in other public forums. But as long as he or she doesn’t violate federal law, a president’s power is most pronounced when it comes to protecting the country’s borders. Even though the Supreme Court deadlocked 4 to 4 earlier this year over Obama’s sweeping immigration plan, which exempted many undocumented immigrants from deportation (and, as a result, left an injunction in place against the administration), the court has previously yielded great authority over the control of the borders to presidents. In 1892, in Nishimura Ekiu v. United States, the court stressed that, while Congress sets the conditions for citizenship, “the final determination of those facts may be entrusted by Congress to executive officers. . . [the executive officer] is made the sole and exclusive judge of the existence of those facts.” The court has also maintained, in United States ex rel. Knauff v. Shaughnessey, that the right to exclude aliens “is inherent in the executive power to control the foreign affairs of the nation.” Finally, while the executive branch is required to follow rules affording due process, the court has held that “whatever the procedure authorized by Congress is, it is due process as far as an alien denied entry is concerned.” While the court imposed a limit in Zadvydas v. Davis in 2001 on how long an alien can be held without deportation, the conditions for entry into the country are set by Congress but implemented by the president.

In that context, the concept of a litmus test based on civic values is quite different from Trump’s previous proposal of a threshold test based on faith — his widely condemned Muslim ban. For starters, one of the civic values that would be evaluated is a visa applicant’s views on the free exercise of religion. And unlike the earlier proposal, this idea is more likely to resonate with those who fear immigrants who come to the United States for economic benefits but who oppose core rights of free speech, freedom of religion, equality of women, LGBT citizens and others.

Trump isn’t alone in raising such concerns. There is rising opposition in the West to increased immigration by Muslim refugees seen as bringing with them extreme Islamic values opposed to the foundations of Western civilization. Although Muslims constitute about 7.5 percent of the French population, in a recent poll, 63 percent of French people think Islam “is not compatible with French values.”

Though many Muslims fled Islamic authoritarian regimes in search of freedom, immigration skeptics cite polls showing support for extreme views among Muslim immigrants, including the imposition of the medieval sharia legal system. A British poll found that 52 percent of Muslims felt homosexuality should be illegal, and almost a quarter supported the introduction of sharia law in England. After opening her country’s doors to thousands of Middle Eastern refugees, even popular politicians such as German Chancellor Angela Merkel are facing increased opposition over the influx of refugees viewed as hostile to Western values.

Polling suggests that many Muslims around the world believe their faith trumps national law — they’re not the only ones. Last year, then-presidential candidate Sen. Marco Rubio said, “We are clearly called, in the Bible, to adhere to our civil authorities, but that conflicts with also a requirement to adhere to God’s rules.” When “those two come in conflict, God’s rules always win.” If similar views were expressed by a Christian immigrant, it would be difficult to see how our bureaucracy would distinguish between this view and the views of Muslim immigrants without maintaining a bias solely against Islam.

Of course, Congress holds the primary authority to determine the requirements for naturalization, and it may have some serious qualms about a new barrier to both entry and eventual citizenship. Once immigrants become American citizens, they’d have every right to advocate for a sharia law system or laws supporting religious values. Those laws should be struck down absent a constitutional amendment, but clearly, Americans have the right to try to convince other Americans that they should abandon core constitutional protections. On that same logic, in 1987, Congress sought to stop the deportation of people for statements that, “if engaged in by a United States citizen in the United States, would be protected under the Constitution of the United States.” Trump’s plan cuts the other way, and many citizens would have difficulty passing his litmus test when it comes to issues such asLGBT rights. There are, after all, a sizable number of Americans who view homosexuality as immoral, and some still support the criminalization of such relations. Of course, as citizens, they’re subject to no such test. Similarly, some Muslim Americans may prefer sharia law and look to one of the many private Islamic courts in this country, just as some Jewish citizens have voluntarily used a system of Jewish courts for more than a century. The difference is that these systems “supplant” conventional law only on a voluntary basis.

Trump’s proposal poses logistical problems that go beyond legal or political considerations. Extensive investigations of the social media accounts and personal backgrounds of immigrants is likely to slow legal immigration to a crawl and massively increase the costs of immigration enforcement. Given, though, the growing unease over illegal immigration both inside and outside the United States, many Americans could probably be convinced of the need to beef up resources for the agencies involved or at least slow down the pace of entry to allow for heightened background checks.

Regardless of the feasibility of Trump’s plan, Hillary Clinton’s camp would probably like to avoid this debate by dismissing the proposal on constitutional grounds — it would save her from having to defend an opposing view and reinforce the narrative that Trump’s worldview is generally out of bounds. But in advancing a litmus test for entry, a President Trump would be claiming the same unilateral authority so willingly yielded to Obama on immigration over the past eight years. Obama has asserted sweeping, unilateral authority in his opposition to state laws seeking to force deportations. Democrats, including Clinton, enthusiastically supported Obama’s assertion of such unilateral powers in exempting undocumented immigrants from deportations. In doing so, they have laid the foundation for Trump to push for the inverse of those policies. It would be difficult, now, for Clinton to claim that Trump cannot use the same unilateral powers to reduce entries as opposed to deportations.

Indeed, as a longtime advocate of unilateral executive power over immigration and foreign policy, Clinton would be hard-pressed to challenge Trump’s authority to impose such tests absent a conflict with federal law. With this proposal, then, Trump may have found an issue that not only threads the constitutional needle with the courts, but moves the political needle with voters.

Jonathan Turley is the Shapiro Professor of Public Interest Law at George Washington University.