Perfectly valid question that hasn’t been asked for 67 years.
One concern is what use is it?
Does anyone believe that illegals or legal aliens are all going to give an honest answer?
If it is in their interest (voting, staying here) they will say “YES I AM AN AMERICAN CITIZEN”.
It is illegal to knowingly and willfully make any false statement to the US government agency/officer. 18 U.S.C. § 1001, is very broad and can apply to any form you sign and submit to the US government.
Is there a legal standard for truthfulness when a person responds to the census questionnaire?
Match the response, site address, voting records, USDA Snap, and outstanding warrants....Bingo! A short list for ICE.