Trump's memorandum argues that the term "persons in each state" has been interpreted to mean "inhabitants of each state", and argues that because undocumented immigrants can only remain in the USA temporarily, that they should not be included in the count.
Dale Ho, an attorney with the American Civil Liberties Union, vowed litigation.
"No one ceases to be a person because they lack documentation", James said.
A MI school district fired a popular high school teacher and coach after he pointed out that "Trump is our president" on social media. The Supreme Court blocked Trump in that fight and it was not included.
"We'll see him in court, and win, again", he said, referring to the earlier citizenship question case.
The ACLU has already promised to challenge Tuesday's directive, as it did with Trump's citizenship question.
What they're saying:In a statement, Trump claimed there "used to be a time when you could proudly declare, 'I am a citizen of the United States.' But now, the radical left is trying to erase the existence of this concept and hide the number of illegal aliens in our country".
The financial and political stakes in the 2020 Census are huge, with Democratic-leaning metropolitan areas with large immigrant populations anxious about losing dollars and political representation through Trump's efforts. "If people are in our country in violation of federal law, why should the states in which they reside benefit from such violations of federal law?"
Since the first USA census in 1790, both US citizens and noncitizens - regardless of immigration status - have been included in the country's official population counts.
"Trump's unlawful effort is created to again inject fear and distrust into vulnerable and traditionally undercounted communities, while sowing chaos with the census", she said. The administration hopes that will help it determine how many people are in the USA illegally.
"His latest attempt to weaponize the census for an attack on immigrant communities will be found unconstitutional", said Ho.
Democratic members of Congress called the president's memo an effort to depress participation in the 2020 census, especially in minority communities.
"Including these illegal aliens in the population of the State for the goal of apportionment could result in the allocation of two or three more congressional seats than would otherwise be allocated", the memo said. It's racist and anti-immigrant and would deny people fair representation in Congress.
Census data is used to determine the size of electoral districts that supply lawmakers to Congress as well as state legislatures.
Trump's memo Tuesday is an blatant attempt to suppress the growing political power of Latinos in the USA, said Thomas Saenz, president and general counsel of the Mexican American Legal Defense and Educational Fund.