A clue

Here is why Roberts rejected the citizenship question:

Although each US government agency is constituted within one branch of the government (judicial, legislative, or executive), an agency's authority often extends into the functions of other branches. Without careful regulation, that can lead to unchecked authority in a particular area of government, violating the separation of powers, a concern that Roosevelt himself acknowledged. To provide constitutional safeguards, the APA creates a framework for regulating agencies and their roles. According to the Attorney General's Manual on the Administrative Procedure Act, drafted after the 1946 enactment of the APA, the basic purposes of the APA are the following:^[9]

1. to require agencies to keep the public informed of their organization, procedures and rules;
2. to provide for public participation in the rulemaking process, for instance through public commenting;
3. to establish uniform standards for the conduct of formal rulemaking and adjudication;
4. to define the scope of judicial review.

The APA's provisions apply to many federal governmental institutions. The APA in 5 U.S.C. 551(1) defines an "agency" as "each authority of the Government of the United States, whether or not it is within or subject to review by another agency," with the exception of several enumerated authorities, including Congress, federal courts, and governments of territories or possessions of the United States.^[10] Courts have also held that the U.S. President is not an agency under the APA. Franklin v. Mass., 505 U.S. 788 (1992).

The Final Report organized federal administrative action into two parts: adjudication and rulemaking.^[8] Agency adjudication was broken down further into two distinct phases of formal and informal adjudication. Formal adjudication involve a trial-like hearing with witness testimony, a written record, and a final decision. Under informal adjudication, agency decisions are made without these formal procedures, instead using "inspections, conferences and negotiations." Because formal adjudication produces a record of proceedings and a final decision, it may be subject to judicial review. As for rulemaking resulting in agency rules and regulations, the Final Reportnoted that many agencies provided due process through hearings and investigations, but there was still a need for well-defined uniform standards for agency adjudication and rulemaking procedures.

This rule is kind of a formalization of due process, and no doubt has caused litigations in the past.

 I missed this part. But the conditions are easily met. Trump need only open some public hearing and list the reason why he wants to count citizens. Hence, Trump will delay the census and execute the formal meetings, then add the citizenship question. The opposition says the citizenship question causes changes in federal funding as latinos might not answer. But asking about citizenship is non racial. Further, it is Congress who sets the rules on fund disbursement, not the census department.

So, pay attention Kevin Drum, and we note that Roberts ruled on this act, not the citizenship question itself. So, cut out the talking point knee jerking, it makes you look stupid.