A Citizenship Question on the 2020 Census: Why Is That a Big Deal?

It was announced this week by the Commerce Department that the 2020 Census would be changed to add a question about citizenship.
Already the state of California has sued, saying the question violates the Constitution; the New York Attorney General has said he will lead a multi-state lawsuit to preserve what he said was a fair and accurate Census.

Why does it matter, and what will it mean for North Carolina — and the country — economically and politically?