WASHINGTON--The U.S. Supreme Court on Thursday handed President Donald Trump a stinging defeat, blocking his contentious citizenship question planned for the 2020 census because officials gave a "contrived" rationale and prompting Trump to suggest an extraordinary delay in the constitutionally mandated population count.

  Conservative Chief Justice John Roberts wrote the 5-4 ruling, joined by the court's four liberals, that will make it difficult for the Trump administration to add the query even if officials offer a new explanation for its need, with the clock ticking toward the deadline for printing the census forms.
  The court upheld a key part of a federal judge's January decision barring the question in a victory for a group of states including New York and immigrant rights organizations that challenged the legality of the administration's plan.
  Critics have called the citizenship question a Republican ploy to scare immigrants into not taking part in the decennial population count and engineer an undercount in Democratic-leaning areas with high immigrant and Latino populations. That would benefit non-Hispanic whites and help Trump's fellow Republicans gain seats in the U.S. House of Representatives and state legislatures, the critics said.
  Trump said he is exploring whether the census, which the U.S. Constitution requires be carried out every 10 years, can be delayed. "I have asked the lawyers if they can delay the Census, no matter how long, until the United States Supreme Court is given additional information from which it can make a final and decisive decision on this very critical matter," Trump wrote on Twitter.
  The census launch date - April 1 - is written into a federal law called the Census Act, known as Title 13. To delay the 2020 census without running afoul of federal law would require Congress to change the law, according to Margo Anderson, a U.S. census historian and professor at the University of Wisconsin at Milwaukee. Delaying the census by executive action would be unprecedented, Anderson added.
  Trump's administration has told the courts that its rationale for adding the question was to better enforce a law that protects the voting rights of racial minorities. Critics called that rationale a pretext, with the Supreme Court's majority embracing that theory.
  Roberts said that under a U.S. law called the Administrative Procedure Act, the federal government is required to give a reasoned explanation for its actions. Roberts said the sole stated rationale - enforcement of the Voting Right Act - "seems to have been contrived" and was "more of a distraction."
  "We are presented, in other words, with an explanation for agency action that is incongruent with what the record reveals about the agency's priorities and decision-making process," Roberts wrote.
  "Accepting contrived reasons would defeat the purpose of the enterprise," Roberts added.
  The court ruled against the challengers in a separate 5-4 vote, with all the conservative justices in the majority, that the Constitution does not in theory prevent the administration or a future one from adding a citizenship question.