The Supreme Court agreed to hear the census citizenship case. Here’s why that matters.

Department of Commerce Secretary Wilbur Ross announced in March that a question about citizenship would be added to the 2020 Census. Wide-ranging opposition followed — from local and state government officials, members of Congress and former Census Bureau directors, all citing consequences for decades to come. Historically, the Census Bureau has worked to guarantee the most accurate count of the entire United States population, notwithstanding citizenship. Census-recorded data has been used to determine how to draw congressional districts, allocate federal funds, and for national disaster and epidemic preparedness.Ross, embroiled in a multistate lawsuit to block the question, has been accused of adding it for partisan purposes. Key issues in the case have made their way to the Supreme Court.The census, which is mandated by the Constitution, may be necessary to a well-functioning democracy, but can this last-minute addition to the survey truly have such dramatic costs?Yes, and one that affects all U.S. residents, including legally documented populations.The most commonly discussed consequences of an undercount are its effect on congressional districts and federal funding. Robert Shapiro, senior policy fellow at the Georgetown University McDonough School of Business, estimates that more than 24 million people could avoid the 2020 Census to keep their information from being shared with law enforcement. This would affect federal programs, such as Medicaid, Section 8 Housing and school lunch programs.