This morning, the Supreme Court heard oral argument in Department of Commerce v. New York concerning whether the plan to include a question on citizenship on the 2020 census violated either the Administrative Procedures Act (APA) or the Constitution's enumeration clause.  Solicitor General Noel Francisco represented the United States in defense of adding the question, and three advocates argued on behalf of Democrat-controlled states, liberal organizations, and the U.S. House against including the question.  

Why is the Trump Administration seeking to include a citizenship question on the census in the first place?  The Republican National Committee and National Republican Congressional Committee succinctly summarized its importance for redistricting in their amicus brief:

Amici curiae are interested in the lawful administration of the Voting Rights Act of 1965, 52 U.S.C. § 10301, et seq., formerly 42 U.S.C. § 1973 (“VRA”) and the challenges state legislators and other redistricting authorities face in creating legally compliant districts.  Because Citizen Voting Age Population (“CVAP”) is widely accepted as the best measure of minority voting power, the Government must be able to gather and disseminate the best available data regarding citizenship. The only reliable, accurate, and consistent method to collect citizenship data useable for redistricting purposes is through the inclusion of the Citizenship question on the short-form Census questionnaire. The previously-used short-form Census questionnaire is insufficient to determine CVAP as necessary for redistricting purposes. All other basic demographic information necessary to construct VRA-compliant districts – total numbers, age, race, and ethnicity – is supplied by short-form Census data. Unless this Court approves the decision of the Secretary of Commerce (“The Secretary”) to place a citizenship question on the 2020 Census, CVAP will be the only critical piece of redistricting information that will need to be derived from sampled data and released with an estimated value suffering from a substantial margin of error.

Seventeen states also filed a strong amicus brief outlining the importance of including this question for improving compliance with the Voting Rights Act.

The justices asked many questions about the statistical questions for which there are not very definite answers: What percentage of people will fail to respond to the census due to the inclusion of a citizenship question? What percentage of non-respondents will fail to respond for another reason? How would the inclusion of a citizenship question affect the accuracy of census data?

In response to questions from Justice Sotomayor, Solicitor General Francisco noted that if it were unlawful to include the citizenship question on the census, it would likewise be unlawful to include it on the American Community Survey, on which it has been included for years.  He also argued that the applicable standard was whether Commerce Secretary Wilbur Ross' decision was reasonable:

And sex and age information, which we ask on the census, is also available in administrative records. Indeed, administrative records are more accurate with respect to sex and age because, presumably, your birth date and your sex don't change over the course of time, whereas your citizenship status does.

So, if you really think that [13 U.S.C.] 6(c) is a problem, we can't ask it on the ACS and we can't ask sex and age on the census, so that's why I think that is plainly wrong. It really does boil down to whether the Secretary's judgment here is a reasonable one.

And in the face of two competing possibilities, either asking the question, getting answers for two-thirds of the people for whom no administrative records existed, at 98 percent accuracy, or using an estimation model that had not yet been created and had an unknown error rate, the Secretary reasonably chose to go with the bird in the hand. . . .

Secondly, there's no evidence in this record that the Secretary would have asked this question had the Department of Justice not requested it. And there's no evidence in this record that the Secretary didn't believe that the Department of Justice actually wanted this information to improve Voting Rights Act enforcement.

All the justices were very skeptical of the U.S. House Democrat's challenge to the question's inclusion, because Congress has the power to control the content of the census but has chosen not to change the broad delegation of power to the Commerce Department.  Justice Kavanaugh pointed out that Congress could have prohibited a citizenship question as it prohibited questions regarding religion.  Justice Ginsburg asked pointedly:

Congress has the primary control over what the census will be, not the executive, and Congress has been alerted to this citizenship question for some time, and it has done nothing about it. So one question is who should decide? Congress is silent. Should the Court then step in?

The House's counsel only response was that Trump Administration officials had refused to appear before Congress and testify, but Justice Roberts pointed out that the challengers had argued that:

[T]here was no basis for the Secretary to make any decision, other than the recommendation that was submitted to him by the Bureau, because that's the evidence. That's the scientific evidence. And so there's no room for the exercise of any discretion.  So what information -- what more information does the Congress need to address the problem? 

On a Federalist Society teleforum call today, Prof. John Baker noted how extraordinary it is that there exists a “presumption of bad faith on behalf of this administration in the minds of certain judges.”  The lower court rulings against the inclusion of the citizenship presumed bad faith on the part of Secretary Ross and other Trump Administration officials to justify finding the citizenship question unlawful.  As the United States noted in its brief, the district court assumed bad faith based on the same reasons it decided that the decision was arbitrary and capricious (citations omitted):

The district court also erred in allowing respondents to seek, and in relying in part on, evidence outside the administrative record. Although courts may stray outside the administrative record when there is “a strong showing of bad faith or improper behavior” on the part of the agency decisionmaker, respondents did not make that showing here. The court’s contrary conclusion was based on precisely the same circumstances it used to bolster its erroneous findings that the Secretary’s decision was arbitrary and capricious and pretextual. Accordingly, they fail for the same reasons. 

Prof. Baker and Ken Klukowski also noted during the call that the essence of the challengers' argument from an administrative perspective is that an administrative decisionmaker can never discount the conclusions of agency experts (i.e. career bureaucrats) or reach a different conclusion without the decision being deemed arbitrary and capricious under the APA.

Observers agree that the five conservative justices appeared skeptical of the challenge to the question's inclusion.  The Court granted certiorari to hear this case directly from the district court because the Census Bureau needs to start printing census forms for next year in June, so a decision is expected soon (in Supreme Court terms).