“I think it is very important to find out if somebody is a citizen as opposed to an illegal,” Trump said. “It is a big difference to me between being a citizen of the United States and being an illegal.”

Trump has insisted on asking about citizenship to the consternation of critics and constitutional experts who say that adding such a question would lead to decreased responses and inaccurate counts. The Constitution mandates regular censuses that count all residents of the country — not only citizens — in order to determine their representation in Congress. An inaccurate count could lead to disproportionate representation in the House and alter district lines.

The president’s critics have also argued that adding such a question would lead to a chilling effect among immigrants who might fear increased government attention to their citizenship status. The Trump administration has formally argued that the citizenship question will help in carrying out anti-discrimination portions of the Voting Rights Act of 1965.

The legal fight over the question made its way to the Supreme Court, which last week sent it back to lower courts to handle. Trump reacted to the Supreme Court’s actions in a rage, saying on Thursday that he would try to delay the census for however long it took for the high court to make a final decision.

Federal law requires the census to be taken “as of the first day of April” 2020.