https://www.breitbart.com/politics/2019/02/15/supreme-court-to-decide-if-census-can-check-u-s-citizenship/
Supreme Court to Decide if Census Can Check U.S. Citizenship
Constitution commands in Article I, Section 2, that every ten years the U.S. government will conduct a nationwide census, and that congressional seats will be apportioned among the states based on those numbers. The Constitution mentions the census again in Article I, Section 9, Clause 4.
The Supreme Court long ago handed down a series of cases holding that the Equal Protection Clause of the Constitution’s Fourteenth Amendment requires that every state and federal legislative district within each state must represent the same number of people. The Court characterized this rule as, “One person, one vote.” Those district lines are likewise based on census data.
But if that means equal political representation, then some argue that each lawmaker should represent an equal number of American citizens, rather than all persons – which include aliens, both legal and illegal. In 2016, the Supreme Court in Evenwel v. Abbottleft answered the question of whether states could draw their district lines based on citizenship instead of total population until a state took that option and someone challenged it in court.
Given that district lines must be based on census numbers, no state could ever try such an option if the census cannot ask if each person it is counting is a citizen.
The census in the past frequently asked if each person was a citizen. The 1820 census was the first to do so, and the most recent one was 1950.