Challengers of census citizenship question tell Supreme Court they have new evidence that shows political motivation

They point to a newly disclosed 2015 study written by Dr. Thomas Hofeller, a Republican redistricting expert, who wrote that using "citizen voting age" population as the redistricting population base would be "advantageous to Republicans and Non-Hispanic Whites."

The challengers, including groups such as the American Civil Liberties Union and Common Cause, say the new information shows Hofeller played a more significant role in the decision to add the citizenship question than has been disclosed and that his study reveals the true motive behind the administration's decision to add the question.

Separately in a letter to District Judge Jesse M. Furman on Thursday, the challengers say the evidence bolsters their argument that while the administration contends the question was added to better comply with federal voting laws, the real reason was to intimidate Hispanic households from being counted.

"The new evidence thus not only contradicts testimony in this case, but it shows that those who constructed the VRA (Voting Rights Act) rationale knew that adding a citizenship question would not benefit Latino voters, but rather would facilitate significantly reducing their political power," the letter to the judge reads.

A Justice Department official said on background that department officials weren't aware of the new document, are looking into the matter and intend to file a response. Hofeller died last August.

Furman ruled against the administration in January, holding that Commerce Secretary William Ross' decision to add the question was unlawful for a "multitude of independent reasons" and must be set aside. He said the decision to add the question violated the Administrative Procedure Act, a federal law that governs the way agencies can establish regulations.

Most critically, Furman who sits on the US District Court for the Southern District of New York, said Ross' stated rationale for the question -- to promote the enforcement of the Voting Rights Act -- was "pretextual -- in other words that he announced his decision in a manner that concealed its true basis."

The Supreme Court agreed to take up the appeal in an expedited time frame and heard arguments in April. In court, the conservative justices appeared ready to side with the government and allow the question.