On the court's final day of decisions before a summer break, the court said the Trump administration's explanation for wanting to add the question was "more of a distraction" than an explanation. The administration had cited the need to improve enforcement of the Voting Rights Act.
After the decision, President Donald Trump tweeted that that ''I have asked the lawyers if they can delay the Census, no matter how long'' until the court can make a final decision.
Seems totally ridiculous that our government, and indeed Country, cannot ask a basic question of Citizenship in a very expensive, detailed and important Census, in this case for 2020. I have asked the lawyers if they can delay the Census, no matter how long, until the.....— Donald J. Trump (@realDonaldTrump) June 27, 2019
.....United States Supreme Court is given additional information from which it can make a final and decisive decision on this very critical matter. Can anyone really believe that as a great Country, we are not able the ask whether or not someone is a Citizen. Only in America!— Donald J. Trump (@realDonaldTrump) June 27, 2019
It's unclear whether the administration would have time to provide a fuller account. Census forms are supposed to be printed beginning next week.
Chief Justice John Roberts had the court's opinion, with the four liberals joining him in the relevant part of the outcome.
A lower court found the administration violated federal law in the way it tried to add a question broadly asking about citizenship for the first time since 1950.
The Census Bureau's own experts have predicted that millions of Hispanics and immigrants would go uncounted if the census asked everyone if he or she is an American citizen.
Immigrant advocacy organizations and Democratic-led states, cities and counties argue the citizenship question is intended to discourage the participation of minorities, primarily Hispanics, who tend to support Democrats, from filling out census forms.
The challengers say they would get less federal money and fewer seats in Congress if the census asks about citizenship because people with noncitizens in their households would be less likely to fill out their census forms.
Evidence uncovered since the Supreme Court heard arguments in the case in late April supports claims that the citizenship question is part of a broader Republican effort to accrue political power at the expense of minorities, the challengers say.
The Constitution requires a census count every 10 years. A question about citizenship had once been common, but it has not been widely asked in the past 70 years. At the moment, the question is part of a detailed annual sample of a small chunk of the population, the American Community Survey.
The case stems from Commerce Secretary Wilbur Ross' decision in 2018 to add a citizenship question to the next census, over the advice of career officials at the Census Bureau, which is part of the Commerce Department. At the time, Ross said he was responding to a Justice Department request to ask about citizenship in order to improve enforcement of the federal Voting Rights Act.
In the other major decision of the day, the court said federal courts have no role to play in policing political districts drawn for partisan gain. The decision could embolden political line-drawing for partisan gain when state lawmakers undertake the next round of redistricting following the 2020 census.
The justices said by a 5-4 vote on Thursday that claims of partisan gerrymandering do not belong in federal court. The court's conservative, Republican-appointed majority says that voters and elected officials should be the arbiters of what is a political dispute.
The court rejected challenges to Republican-drawn congressional districts in North Carolina and a Democratic district in Maryland.
The decision was a major blow to critics of the partisan manipulation of electoral maps that can result when one party controls redistricting.
Roberts also spoke for the majority in this case, saying that the districting plans "are highly partisan by any measure." But he said courts are the wrong place to settle these disputes.
In dissent for the four liberals, Justice Elena Kagan wrote, "For the first time ever, this court refuses to remedy a constitutional violation because it thinks the task beyond judicial capabilities."
The ABC Owned Stations contributed to this report.