President Donald Trump tweeted Monday that the 2020 decennial census would be “meaningless” and “a waste” if it doesn’t contain a question asking people whether they are U.S. citizens.

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

The Trump administration’s decision to add a citizenship question has been met with widespread criticism from advocacy groups and Census Bureau experts. They say the question will cause fewer people ― particularly immigrants and people of color ― to respond to the survey, which every 10 years attempts to count every living person in the United States.

An undercount would have lasting and severe consequences. The census is used to determine how electoral districts are drawn and to help determine how $880 billion in federal funds are allocated each year. Trump’s Monday tweet marks exactly one year until census day, and many groups are already trying to drum up enthusiasm about the decennial count and educate people about the importance of responding.

Data from the decennial census provides essential information to policymakers that has nothing to do with citizenship. State and local governments use the data for planning and businesses use it to make decisions, said John Thompson, who served as director of the Census Bureau from 2013 to 2017. Almost every household survey uses data from the census as a benchmark to make sure their own samples are representative, Thompson said, and inaccurate U.S. Census data would lead to a chain reaction of distorted information for the next decade.

“Large companies, folks in the real estate business, in retail, they are using the intricacies of the population data to make decisions about where they’re going to site a business, if they’re going to open one at all, exactly where should it be to get the best bang for the buck for what they’re trying to do,” said Howard Fienberg, vice president for advocacy at the Insights Association, which represents the interests of the marketing research and data analytics industry. “It’s bread and butter for decision-making for the whole of the private sector in so many ways.”

While different Census Bureau surveys have asked a sample of Americans about citizenship, the decennial survey, which goes out to every American household, has not asked about citizenship status since 1950.

Terri Ann Lowenthal, a census consultant who formerly worked as staff director of the House Census and Population Subcommittee, noted that the Constitution requires the government to count all “persons.” It says nothing, she added, about only counting citizens.

“The president directly contradicts the constitutional mandate for the census, which is to count all people living in the United States regardless of immigration status or citizenship for the purpose of equal political representation,” Lowenthal said in an email. “By suggesting that the census must ask about citizenship to be worthwhile, the president is both making the Census Bureau’s job much harder and potentially sending the nation towards a constitutional crisis that would be triggered if the public loses confidence in the objectivity of the process.”