Yep – that occurred to me too – the census is prescribed by the Constitution, and it is the basis for apportionment of districts. As it is, people get all freaked out about answering even the simplest questions – one could only imagine adding a question about being an eligible voter!
Consider too that even with using the census, undocumented immigrants are sorely under-reported because of fear of deportation. So while those seeking to redistribute power to the gullible might contend this is about the undue influence of illegal aliens in our government (never mind that Citizens United turns a blind eye to foreign interests dumping unrestricted amounts of money into our elections anonymously) that’s a bogus diversion as it always is.
EDIT: thinking about it some more, we have 435 Representatives, divided among the states by state population, and then divided (i.e., gerrymandered) geographically within the states into Congressional districts. So this affects the Federal level, doesn’t it?
States have been gerrymandering for years, but they do it with the number of Reps they’ve been given to work with. We lost a Dem district locally last census cycle because my state lost a seat, and the right wing state house gerrymandered the remainder to squeeze out the Democrat.
Point being, if apportionment by eligible voters is thought to favor Republicans, they must believe enough people now counted in blue states would be eliminated from the process to yield a net gain in House seats to red states. Seems to me states like Texas and Arizona might lose seats in that scuffle, but it’s said Texas anyhow might be turning blue.