This piece originally appeared at Just Security.

According to the Supreme Court, “the clearest command of the Establishment Clause is that one religious denomination cannot be officially preferred over another.” But that command is apparently not clear enough for President Donald Trump. On Friday he signed an executive order on refugees that imposes a selective ban on immigration from seven Muslim-majority countries as well as establishes preferential treatment for refugees seeking asylum who are identified with “minority religions” in their country of origin. In case there was any doubt about the latter provision’s intent, Trump told Christian Broadcast News that it was intended to give priority to “Christians” seeking asylum over “Muslims.”

In both respects, the executive order violates the “clearest command of the Establishment Clause.” First, as I developed in an earlier post, the Constitution bars the government from targeting Islam. One of the lowest of many low moments in Donald Trump’s presidential campaign was his December 2015 call for a “total and complete shutdown” of Muslim immigration. The proposal treated as presumptively suspect a religion practiced by about 1.6 billion people worldwide, nearly a quarter of the globe’s population. Trump soon retreated to talk of “extreme vetting,” but he never gave up his focus on the religion of Islam. Friday’s executive orders are of a piece with his many anti-Muslim campaign promises.

As I wrote earlier, one of the critical questions with respect to the validity of executive action challenged under the Establishment Clause is its intent and effect. If intended to disfavor a particular religion, it violates the Establishment Clause. Here, there is copious “smoking gun” evidence that the president intended to disfavor Muslims on the basis of their religion. It includes:

On December 7, 2015, the Trump campaign issued a press release stating that “Donald J. Trump is calling for a total and complete shutdown of Muslims entering the United States until our country’s representatives can figure out what is going on.”

In July 2016, he effectively admitted that his revamping of the proposal was designed to target Muslims without expressly saying so. In an interview on “Meet the Press: with NBC’s Chuck Todd,” Trump said he would target immigrants from certain countries, but he resisted the suggestion that this was a retreat from his proposal to target Muslims. “I actually don’t think it’s a rollback. In fact, you could say it’s an expansion… People were so upset when I used the word Muslim. Oh, you can’t use the word Muslim. Remember this. And I’m OK with that, because I’m talking territory instead of Muslim.”

In November 2015, Trump told NBC News he “would certainly implement” a database to track Muslims in the United States. “I would certainly implement that," he said. "Absolutely.” Would Muslims be legally required to register? “They have to be — they have to be,” Trump replied.

In March 2016, Trump said, “Frankly, look, we’re having problems with the Muslims, and we’re having problems with Muslims coming into the country.”

Nor is this mere campaign rhetoric. In signing the executive order on Friday, Trump pledged to “keep radical Islamic terrorists out of the United States of America.” Not “terrorists.” Not “radical terrorists.” But only “radical Islamic terrorists.” Of course we should be keeping terrorists out, but why limit our concern to those of one faith?

Second, the flipside of the order, equally invalid, is that it is intended, as Trump candidly admitted on Christian Broadcast News, to favor Christians fleeing persecution over others. Here, too, Trump has violated the Establishment Clause’s “clearest command.” Christians suffering persecution deserve asylum, but so do Muslims suffering persecution and Buddhists and Jews and Sikhs and Zoroastrians. There is no legitimate reason to favor Christians over all others who are persecuted for their beliefs.

The executive order, of course, does not say in express terms that it is favoring Christians and disfavoring Muslims. But Trump is the signatory, and he has said so explicitly. Moreover, even absent that evidence of Trump’s invidious intent, the order on its face favors refugees from “minority religions” over those from “majority religions” in any given country. That distinction independently violates the principle of denominational neutrality, even if in some countries it means we will be privileging Christians and in other countries Muslims.

The law struck down in Larson v. Valente did not name any particular denominations, but it simply imposed differential registration and reporting requirements on religions that received more than half of their total contributions from members and those that did not. Even though the law did not single out a specific religion by name, it failed to treat all denominations the same and therefore violated the Establishment Clause. Thus, even if Donald Trump hadn’t admitted his unconstitutional purpose on TV, the executive order would be unconstitutional.

The notion that it is improper to use religions litmus tests at the border has wide appeal. When Trump initially proposed his Muslim ban in December 2015, Sen. Pat Leahy (D-Vt.) introduced a resolution expressing “the sense of the Senate that the United States must not bar individuals from entering into the United States based on their religion, as such action would be contrary to the fundamental principles on which this nation was founded.” It passed 96-4. (Jeff Sessions, Trump’s nominee for Attorney General, was one of the four holdouts.) It will be interesting to see whether the Republicans continue to oppose religious discrimination now that it’s the official policy and practice of their president, not just the proposal of a maverick candidate.

The ACLU has already filed suit to challenge the executive order, working with the International Refugee Assistance Project at the Urban Justice Center, the National Immigration Law Center, Yale Law School’s Jerome N. Frank Legal Services Organization, and the firm Kilpatrick Townsend & Stockton. The suit was filed on behalf of two Iraqi refugees stopped at John F. Kennedy International Airport on the authority of the executive order, and it argues that the order violates due process, equal protection, international law, and immigration law. We are also preparing an Establishment Clause challenge. As we told President Trump two days after he was elected, if he pursues the many unconstitutional measures he proposed during the campaign, “we’ll see you in court.”