Commentators debating the constitutionality of President Trump’s travel ban—formally, Executive Order 13,780—continue to disagree about whether courts should be focusing on Trump’s motive in ordering the ban. But under existing law, it’s pretty clear that Trump’s motive matters. The case against the travel ban is partly an equal protection claim. In equal protection cases, the actual motive behind the challenged action is indispensable to the analysis. (Equal protection differs in this respect from some other parts of constitutional law, including rational-basis review of legislation and most Fourth Amendment review of police-officer conduct.) In an equal protection case challenging an executive order, the motive that matters is the President’s. Both before and after assuming the Presidency, Trump has made public statements that seem to shed light on his motive for issuing the ban. So reviewing courts should consider those statements.
The logic is pretty simple. But some people are resisting it in this case. They raise questions that might seem troubling. Can it really be that an illicit motivation dooms the order even if the same order could have been issued based on legitimate motives? If the order was issued for a combination of legitimate and illegitimate motives, shouldn’t the fact that there were also legitimate motives be enough to make the order valid? And if Trump’s stated desire to prevent Muslims from entering the United States or his bigoted statements about Muslims more generally make Executive Order 13,780 unconstitutional, would it follow that the Trump Administration will never be able to taken any action that adversely affects Muslims, because legal challengers will always claim discrimination and point to Trump’s already-existing expressions of bigotry as proof?
Those questions raise conceptual issues worth discussing, both in law school classrooms and in public discourse more generally. But as a matter of law, the questions have simple answers. Yes, a legal rule promulgated with unconstitutional motives can be invalid even if the same rule promulgated for legitimate reasons would be valid. If a legal rule is enacted for a combination of legitimate and illegitimate motives, the validity of the rule depends on whether the illegitimate motive was a but-for cause of the rule’s enactment—that is, on whether the rule would have been enacted had the illegitimate motive not been present. And no, an official’s expressions of bigotry at Time 1 do not automatically render all of his subsequent actions in the same issue space unconstitutional. Indeed, such statements do not automatically invalidate anything. But evidence of illicit motive is always relevant.
To see these rules in action, consider then-Justice Rehnquist’s opinion for the Court in the 1985 case of Hunter v. Underwood. Hunter adjudicated an equal protection attack on § 182 of Article VIII of the Alabama Constitution of 1901. Section 182 denied the right to vote to people who had been convicted of any of a certain set of crimes. According to the challengers in Hunter, the list of crimes in §182 was deliberately crafted to disfranchise as many black people as possible: the defendants convicted of the specified crimes, the Alabama convention predicted, would disproportionately be black. And indeed, §182 had that effect, denying the vote disproportionately to black citizens throughout the twentieth century.
Writing for an 8-0 Court, Justice Rehnquist declared that Alabama’s disfranchisement provision violated the Equal Protection Clause. Rehnquist noted that § 182 was racially neutral on its face: the text of § 182 drew no distinction between black and white persons. But a legal rule neutral on its face, Rehnquist continued, would violate equal protection if it had both the purpose and effect of discriminating on the basis of race. Clearly § 182 had a racially disparate effect: it disfranchised far more blacks than whites. So the remaining question was whether § 182 had a racially discriminatory purpose.
Rehnquist acknowledged that it is often hard for a court to establish the purpose for which a legal rule is enacted. Many legal rules are promulgated for more than one purpose. When the enacting institution is a multimember body (as legislatures and constitutional conventions are), courts should be wary of striking down enactments on the basis of what only a few of the participants were motivated by, because most of the decisionmakers might have had perfectly legitimate motives. But in the case at hand, Rehnquist wrote, the Court had no trouble concluding that the 1901 Alabama convention intended to discriminate against African-Americans. Reputable historians had characterized the convention that way, and many convention delegates said openly that they wanted to establish white supremacy in Alabama. In light of the available evidence, Rehnquist explained, the idea that the state convention did not have racist motives would be hard to take seriously.
But the analysis was not finished at that point, because the possibility remained that § 182 was not enacted only for racially discriminatory purposes. According to the lawyer arguing in defense of § 182, the Alabama convention had acted partly for racist reasons and partly for other reasons. So Rehnquist applied the Court’s standard analysis for mixed-motive equal protection cases, an analysis associated with Village of Arlington Heights v. Metropolitan Housing Development Corp. Under Arlington Heights, once a legal rule is shown to have been motivated at least partly by an unconstitutional discriminatory purpose, the government bears the burden of showing that the same rule would have been enacted even if the illicit motive had played no role.
Note that the required showing is not that the government might hypothetically have enacted the same rule in the absence of a discriminatory motive. Instead, what the government must show is that the same rule would actually have been enacted without the discriminatory motive. The question is how this rule came to be, not whether such a rule could come about in some other way. Rehnquist summed it up this way: “Without deciding whether § 182 would be valid if enacted today without any impermissible motivation, we simply observe that its original enactment was motivated by a desire to discriminate against blacks on account of race and the section continues to this day to have that effect. As such, it violates equal protection.”
The parallels to the travel ban case are obvious. The text of Executive Order 13,780 does not distinguish between Muslims and non-Muslims. But the people whose entry into the United States would be blocked by the Order are overwhelmingly Muslim. So the equal protection question is whether a desire to prevent Muslims in particular from entering the United States motivated the President to issue the Order. The answer to that question, I think, is pretty much as clear as the answer to the question of whether the 1901 Alabama convention was motivated by a desire to prevent blacks from voting. At the very least, Trump’s repeated statements both before and after assuming the Presidency are evidence that Trump saw the travel ban order as a way to prevent the entry of Muslims in particular.
Supporters of the Order sometimes argue, though, that the government could have banned travelers from the six specified countries for legitimate national security reasons. Perhaps that’s true: I don’t have sufficient security expertise to know for certain. But even supposing that the government could in principle have instituted something like Executive Order 13,780 for legitimate reasons, does anything follow about the constitutionality of the Order that was actually promulgated? The Order’s supporters say yes—that if the President could have banned travel from these countries for legitimate reasons, the Order is valid, regardless of the actual motives on which he acted. But that’s not how equal protection analysis works. As Rehnquist explained in Hunter, the question is not whether the challenged rule would be valid if it had been enacted for legitimate reasons. It’s whether an illegitimate motive was a but-for cause of the rule’s actual enactment.
For the same set of reasons, invalidating the travel ban because it was enacted with a discriminatory motive would not imply that any action the Trump Administration ever takes that has a disparately adverse effect on Muslims would also be unconstitutional. The question in such a future case would be the same as the question in the travel ban case, or, for that matter, as the question in Hunter. Was the enactment of the particular rule in question actually motivated, in whole or in part, by illicit prejudice? The fact that Trump made statements in 2015, 2016, and 2017 suggesting that his Islamophobia motivated his desire for a travel ban would not necessarily prove that, say, some executive order issued late in a second Trump Administration on an issue other than immigration was also motivated by anti-Muslim prejudice. The question, then as now, would be one of fact: what were the motives behind this particular enactment?
One might wonder whether it matters that the travel ban case concerns a decision by the President rather than by a constitutional convention (as in Hunter) or a zoning board (as in Arlington Heights). There are two ways in which the distinction might be important. First, it is easier to impute motivations to individual persons than to multimember bodies. So it is less problematic to reason from bigoted statements by a President to the conclusion that the President acted for bigoted reasons than it is to reason from bigoted statements by members of a convention (or a zoning board, or a legislature) to the conclusion that a rule promulgated by that multimember body was illicitly motivated. To be sure, individuals as well as groups often act on the basis of mixed motives, and executive branch decisionmaking usually involves the input of many minds. But an executive order is issued on the authority of one single person. If that person acted wholly on the basis of a discriminatory motive, his order is invalid. If he acted partly on the basis of a discriminatory motive, his order is invalid unless the government can demonstrate that he would have done the same thing even without the discriminatory motive.
The other possible way in which it might matter that the travel ban case is about the President concerns the matter of deference to executive decisionmaking on matters involving national security, immigration, and foreign affairs in general. The judicial practice of deference in these areas is real, important, and generally sensible.
But judicial deference to executive decisionmaking means that judges are loath to second-guess Presidents as to the policy wisdom of the relevant decisions, largely on the ground that the President has superior resources for assessing the complicated policy spaces involved. It does not mean that judges are supposed to pretend not to know why the President has taken an action even when the President has more or less announced his reasons. Nor does it mean that courts are supposed to defer to the President when he claims that he would have taken a particular action even if he didn’t have an unconstitutional motive that he does happen to have. After all, to defer to the President on that question would be to exempt him completely from the requirements of equal protection. Any President who acted for reasons of invidious prejudice could protect his actions from constitutional attack merely by asserting in court that he would have done the same thing for other reasons.
A final parallel with Hunter is worth mentioning here. Apparently aware that something like the travel ban might face constitutional obstacles, President Trump reportedly asked his advisors to figure out “the right way to do it legally.” One might think that this approach should demonstrate that whatever Trump’s attitudes about Muslims might be, the actual purpose of his Executive Orders is constitutionally sound, because he specifically sought to pursue his ends in a way consistent with governing law. And I suppose there is an important way in which a government official who thinks of the law as a constraint on how he can implement his bigotry is better than a government official who thinks he can implement his bigotry without caring about what the law might require. But as Hunter demonstrates, the intention to act legally cannot save an enacted rule if the enacting authority was in fact motivated by a purpose prohibited under the Equal Protection Clause.
As Justice Rehnquist noted, the president of Alabama’s 1901 constitutional convention also stated an intention to act only as the law permitted: “[W]hat is it that we want to do? Why it is within the limits imposed by the Federal Constitution, to establish white supremacy in this State.” Yes, the Alabama convention wanted to establish white supremacy, but, if one takes this statement seriously, its president specifically said that the convention sought to pursue that goal only within what the U.S. Constitution would permit—just as President Trump reportedly sought to implement a Muslim ban in a way that would be legal. But there is no such thing in equal protection doctrine as pursuing an unconstitutional purpose constitutionally, because it is the purpose itself that makes an action unconstitutional (assuming, of course, that the action succeeds in having a disparately adverse effect on the targeted group).
If you are really serious about wanting not to violate the Equal Protection Clause, the way to do it isn’t to look for acceptable ways to translate your discriminatory motives into government policy. It’s not to act on the basis of discriminatory motives.
Richard Primus is the Theodore J. St. Antoine Collegiate Professor at the University of Michigan Law School
Follow him on Twitter @Richard_Primus
 See, e.g., Whren v. United States, 517 U.S. 806 (1996) (explaining that the constitutionality of a police seizure under the Fourth Amendment would be measured by reference to what a reasonable officer in the situation might have intended rather than what the particular officer in the situation actually intended and that challenges alleging actual discriminatory motives on the part of the particular officers should be adjudicated as issues of equal protection).
 See Village of Arlington Heights v. Metropolitan Housing Development Corp., 429 U.S. 252 (1977).
 471 U.S. 422 (1985).
 Hunter, 471 U.S. at 229 (quoting John B. Knox, president of the Alabama constitutional convention of 1901).