Last weekend, tens of thousands of people around the country marched for science, celebrating the role it plays in our daily lives and encouraging politicians to rely on science in making regulatory and policy decisions on a host of issues. Central to this celebration of science was also the idea that facts matter. It’s an important principle, and one that’s no less true in law than it is in science.

When judges decide cases, their decisions are often shaped, in critical ways, by their understanding of the facts—and not just facts about the parties and what happened to them. As I have discussed elsewhere, there are two types of facts that can play a critical role in judicial decisions: adjudicative facts—the who, what, and when of any lawsuit—and legislative facts, more general facts about the way the world works.

Because judges’ decisions so often depend, sometimes expressly and sometimes not, on legislative facts and their understanding of how the world works, a misunderstanding about the way the world works—a perception that is at odds with empirical reality—can produce troubling results. In Shelby County v. Holder, for example, the Supreme Court gutted a key provision of the Voting Rights Act—the requirement that changes in voting laws be precleared by the Department of Justice or a federal court—because, in the Courts’ view, the law “‘impose[d] current burdens‘” that could not be “‘justified by current needs.’” In other words, in the Court’s view, there had been such tremendous progress in combatting racial discrimination in voting in the states covered by the preclearance requirement that the preclearance requirement could no longer be justified. The Court’s factual understanding that voting discrimination in the covered jurisdictions had been largely addressed was thus critical to its decision. In dissent, Justice Ginsburg noted that Congress “was of another mind” and had developed a “voluminous record” to support the preclearance requirement’s continued operation.

It’s not difficult to imagine cases that may soon be before the Court in which legislative facts will be critical to the Court’s decision. Consider the challenges to President Trump’s Muslim ban. The Trump Administration has defended the law on, among other bases, the ground that there are national security justifications for it. Whether that is so is a factual, empirical question. (One important data point in answering that question: since at least 1975, not a single American has been killed by a terrorist attack on U.S. soil carried out by individuals born in the six countries that are the subject of the order.) Or consider a challenge to a restrictive abortion law. Whether the law places an undue burden on women is going to depend on, among other things, to what extent the restriction makes it more difficult for women to access abortion. That, too, is a factual, empirical question. Or consider, finally, a challenge to a voter ID law. Whether that law can be justified will depend on whether there is a real problem with impersonation voter fraud that the law addresses. Again, that is a factual, empirical question. (For a compelling account that there generally is no such problem, see this.)

When the Supreme Court and courts of appeals are deciding cases, they are sometimes able to rely on a factual record developed by a trial court; but often, especially when it comes to legislative facts, appellate courts rely on information produced by the parties and amici in their briefs. It is thus critically important that the courts be able to trust the facts offered in those briefs, including by the Department of Justice. While the Department of Justice obviously comes to any litigation with a particular position it is advancing, one of its guiding principles is “‘to do equal and impartial justice to all its Americans.” Moreover, as a repeat player before the federal courts, the Department of Justice has historically strived to ensure that it has credibility with the judges and justices before whom it regularly appears.

Just 100 days into the Trump Administration—the Administration that gave rise to the concept of #AlternativeFacts—there is reason to worry that facts don’t matter to the Justice Department now led by Trump’s Attorney General, Jeff Sessions. Consider just a few examples. As Leah Litman has written on this blog, the Department of Justice brief in the Fourth Circuit case involving the President’s Muslim ban criticized the district court for placing too much emphasis on statements made by Trump the candidate, rather than Trump the President, saying that “‘[v]irtually all’” or “‘[n]early all’” of the statements on which the court relied were made before the President took office or formed a new Administration.

According to Litman, “these statements rang a bit hollow, to put it mildly. To put it precisely, I would say these statements rang flat out untrue.” As she showed, a majority of the statements on which the district court relied were, in fact, actually made after the Inauguration. (It’s worth noting that there’s also reason to question DOJ’s efforts to lump all pre-Inauguration statements into one category. All of Trump’s statements are relevant to the question of motive in the Muslim ban case, but even if one decided to discount statements made by candidate Trump, statements made by President-elect Trump after he was elected and while he was forming his Administration are surely relevant.)

Also writing for this blog, Neil Kinkopf has written about “[a]lternative [f]acts” in the Department of Justice’s brief in the case involving a challenge to the constitutionality of the leadership structure of the Consumer Financial Protection Bureau. As he explains, the DOJ brief states that the executive branch has “‘consistently objected’” to “‘limitations on the President’s authority to remove a single agency head.’” This, he says, is “patently wrong,” noting, for example, that President Obama “actively supported [the CFPB’s] establishment as an independent agency,” and that “no President has objected to the limit on removal authority with respect to the Director of the Federal Housing Finance Agency.”

Finally, just last week, the Department of Justice sparked controversy when it sent a letter to a number of cities around the country, threatening to withhold federal funds unless they can show that they are complying with a federal immigration law. At the same time, the Department of Justice issued a press release in which it noted that “many of these jurisdictions are . . . crumbling under the weight of illegal immigration and violent crime.” In particular, it described New York City’s problems with “gang murder” as “the predictable consequence of the city’s ‘soft on crime’ stance.” However, as New York City’s Mayor pointed out in response, New York “just marked its safest three months in history.”

In sum, the Sessions Department of Justice is not developing a strong track record when it comes to presenting facts fairly and honestly. If it continues on this course, it will likely undermine its credibility with the judges whom it is trying to persuade. And that’s as it should be, because facts matter, whether this Administration realizes it or not.