President Donald Trump defended the controversial citizenship question on the 2020 census on Wednesday.

“The American people deserve to know who is in this Country,” Trump wrote on Twitter. “Yesterday, the Supreme Court took up the Census Citizenship question, a really big deal.”

The Supreme Court heard arguments on the legal case after the Southern District of New York sided with leftist lawsuits trying to block the question from being included in the census.

The question will ask participants if they are American citizens. Leftists argue that the citizenship question will cause illegal immigrants to be unwilling to participate in the census.

The Supreme Court heard opening arguments on the case on Tuesday.