U.S. President Donald Trump on Monday injected himself into one of the most consequential cases of the current Supreme Court term, saying the nation's 2020 census would be "meaningless" without adding a citizenship question to the questionnaire.

The comment on Twitter came ahead of an expected ruling from the Supreme Court on whether Commerce Secretary Wilbur Ross' decision to add the citizenship question violated federal law.

"Can you believe that the Radical Left Democrats want to do our new and very important Census Report without the all important Citizenship Question," Trump tweeted. "Report would be meaningless and a waste of the $Billions (ridiculous) that it costs to put together!"