U.S. Census Bureau

President Trump threatened to delay next year's constitutionally mandated head count hours after the Supreme Court ruled to keep a citizenship question off 2020 census forms for now.

Close to a half-million households in most of the U.S. are receiving letters for a last-minute experiment gauging how adding a citizenship question could affect how people respond to the 2020 census.

Never before has the U.S. census directly asked for the citizenship status of every person living in every household. The question the Trump administration wants on the 2020 census could change that.

The U.S. Supreme Court heard oral arguments Tuesday on a citizenship question proposed for the 2020 census. The court's ruling could affect Ohio in several ways. The state is expected to lose a congressional seat and an electoral vote after the 2020 Census, due to population declines. Those seats are apportioned on the basis of all residents in a state, not just citizens.

The justices are weighing whether the Trump administration can include a citizenship question on the 2020 census. A decision is expected this summer, when printing of the census forms is set to begin.

The Census Bureau is counting on the Supreme Court to resolve the legal battle by June so that 2020 census forms can be printed. But an appeal in a Maryland lawsuit could complicate that timeline.

Plans to use the 2020 census to ask about U.S. citizenship status suffered another major blow. A ruling in Maryland joins earlier ones in New York and California blocking the citizenship question.

Who gets counted in the 2020 census? What kind of information do households have to give? NPR answers questions about the national head count required by the U.S. Constitution once a decade.

The high court agreed to a speedy review of a lower court's ruling that stopped Trump administration plans to use the census to ask whether every person living in the country is a U.S. citizen.

In focus groups for the U.S. census, some participants identified the citizenship question as a significant reason why they would avoid taking part in the head count.