The express purpose of the census as explicitly mandated in the Constitution is for the purpose of determining apportionment of legislative districts.
Certainly it is also an excellent opportunity to collect additional demographic data that is useful in determining public policy needs, and one could argue that citizenship vs. non-citizenship is useful demographic data.
But if any aspect of collecting demographic data (not the Constitutionally-stated purpose) interferes with the specific, expressed Constitutional purpose by reducing participation, then collection of that data violates the Constitution. The citizenship question is therefore unconstitutional.
The express purpose of the census as explicitly mandated in the Constitution is for the purpose of determining apportionment of legislative districts.
Certainly it is also an excellent opportunity to collect additional demographic data that is useful in determining public policy needs, and one could argue that citizenship vs. non-citizenship is useful demographic data.
But if any aspect of collecting demographic data (not the Constitutionally-stated purpose) interferes with the specific, expressed Constitutional purpose by reducing participation, then collection of that data violates the Constitution. The citizenship question is therefore unconstitutional.