The bitter controversy is about whether the administration can ask any recipient a citizenship issue of the 2020 census for the first time since 1950 – a step that could affect the balance of power in states and the House of Representatives based on the total population. Adding the question, say critics, may result in minorities being subjugated.
The Supreme Court's judgments issued two major cases in their last day of the charges, both of which are about bias. Roberts split his voices, sits with conservatives on a big decision that allows serious partisan gerrymandering and then crosses ideological lines aside with liberals on the census.
"If judicial review is to be more than an empty ritual, it must demand something better than the explanation offered for the action taken in this case," Roberts wrote.
The decision raises the question of whether the administration will have sufficient time or the ability to add the citizenship before the census begins. The administration previously told the court that the questionnaire should be printed before the end of June.
The data obtained from the 2020 Census is used to award congressional sites and the distribution of billions of federal dollars to states and localities over the next decade.
The Trump administration claimed the citizenship issue of the census questionnaire is necessary to better comply with federal voting law. Critics argued that it is an attempt to scare non-citizens and Latin American households and will lead to a decline in response rates and under-representation of minorities.
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Trump tweeted in April, "Can you believe the radical left Democrats will make our new and very important census report without all the important Citizenship Question. The report would be meaningless and a waste of $ Billions (ridiculous) that it costs to put together! "
The administration has also claimed executive privilege over materials related to the citizenship issue and encourages a struggle with house democrats.
Roberts said the explanation for adding the question did not pass patterns.
"The only stated reason – seems to have been constructed. In other words, we are presented with an explanation of the agency's action that is incompatible with what the record reveals the agency's priorities and decision-making."
Justice Stephen Breyer participated in part by Justices Sonia Sotomayor, Ruth Bader Ginsburg and Elena Kagan, agreed with Roberts that the Trade Department provided a "reasonable reason" to add the question. But they would have gone further. They wrote separately to say that the decision violated a federal law, the law of administrative procedures, regulating how agencies set their rules.
Breyer wrote that the question "risked undermining public confidence in the integrity of our democratic system."  New York Attorney General Letitia James, who challenged the administration, said in a statement Thursday that "This one issue could have caused a significant undercount, especially by non-citizens and latinos."
"Thanks to the Court, the census will remain a tool to deliver on our government's promise of justice and justice," James said.
The trading department simply said, "The decision is currently under review."
Justice Clarence Thomas, partially attended by Justices Neil Gorsuch and Brett Kavanaugh, said he would have allowed the question of the census.
"For the first time ever, the Court rejects an agency action solely because it questions the sincerity of the otherwise adequate justification of the Agency," Thomas wrote.
"Recognition of suspicion of mistrust and distrust that seems to characterize modern discourse, the Court declares the secretary's memorandum" pretextual "because" seeing the evidence as a whole "would explain his explanation of including a census citizen question to enforce the law on voting rights … "seems to have been constructed.
Each lower court requested to consider that the issue has blocked the administration from adding the question, stating that Minister of Commerce Wilbur Ross exceeded his authority under federal or constitutional law by doing so.
Steve Vladeck, CNN Supreme Court Analyst and Professor at the University of Texas School of Law, said there might be a big difference between the formal decision and its practical effect given the timing.
"Formally, it is a very narrow deci that is unlikely to have such a direct impact on such cases ahead, and it does not even prevent the Trump administration from asking census citizenship in a way which is less transparent, "he said. "But it will almost be difficult for the government to run the traps in time – and the most likely result is that the 2020 census will go out without a citizenship issue."