MANHATTAN (CN) – A federal judge refused Friday to let the Commerce Department shield a trio of documents that he found critical to its plans to update the 2020 census with a citizenship question.

“This case is of great public importance in my judgment,” U.S. District Judge Jesse Furman said at a hearing this afternoon.

Each of the three documents were either sent or received by Commerce Secretary Wilbur Ross. Currently under seal, Furman said the documents “go to the heart of the central issue” in this case.

Since April, New York Attorney General Barbara Underwood has been leading 18 states and several cities and civil rights groups in a lawsuit accusing Ross of playing politics with the census by slanting it against immigrants of color. An undercount of these populations, which traditionally vote Democratic, would likely reduce the political power and federal funding of blue states for a decade.

To prove a discriminatory motive, Underwood has fought to have Ross testify either at deposition or trial.

Department of Justice attorney Kate Bailey, who called such a request “unprecedented” today, estimated that the government already produced more than 40,000 pages of documents.

But attorney Dale Ho argued for American Civil Liberties Union that the government stonewalled requests for data from 30 focus groups, which confirm fears that the citizenship question would chill participation from immigrants of color.

“The only reason we knew about these documents, your honor, is that we adduced their existence in a deposition,” Ho said.

To believe government that it has no data supporting the study “strain[s] credulity,” the lawyer added.

Though Furman ordered the government to produce this data, too, he said it can still assert any objections – such a privacy of the participants – that have not been waived.

The Commerce Department also has been cagey about identifying the “senior administration officials” whom Ross has cited as raising the citizenship question before he began considering it.

Bailey said the government could not ascertain those officials after making a “reasonable inquiry.”

“Did that reasonable inquiry involve consultation with Secretary Ross?” Furman pressed.

After Bailey replied that it did, Furman quoted the old adage: “One can’t draw blood from a stone.”

The judge did not order the government to provide the information, but he added that this denial could have bearing on whether he orders Ross to face deposition.

On the eve of today’s hearing, Underwood filed a letter informing Furman that a recently disclosed email chain shows that the Commerce Department undertook a “deliberate effort to whitewash the record.”

Sent in August 2017 — months before Commerce Secretary Wilbur Ross announced that the census would for the first time in 50 years include a question about citizenship — the emails show Ross and his deputy, Earl Comstock, describing how to insulate the change from challengers.

“Since this issue will go to the Supreme Court we need to be diligent in preparing the administrative record,” Comstock wrote on Aug. 9, 2017.

“We should be very careful, about everything, whether or not it is likely to end up in the SC,” Ross replied a day later.

Attorney General Underwood told a federal judge Thursday that these emails show Ross should be deposed about what actions his office took to scrub the paper trail.

Since April, Underwood has been leading 18 states, several cities and civil rights groups in calling the citizenship question unconstitutional. Attorneys for this group plan to push for Ross to take the hot seat at a status conference on Friday afternoon.

Another exhibit included in Underwood’s letter is a May 24, 2017, email in which David Langdon, a policy adviser at the Commerce Department, acknowledges that past census counts paid no attention to citizenship status.

“Long story short is that the counting of illegal immigrants (or of the larger group of non-citizens) has a solid and fairly long legal history,” Langdon wrote.

The census has not included a citizenship inquiry since 1950, and its reinsertion has been a priority for the anti-immigrant wing of the Republican Party. Emails previously disclosed during this lawsuit showed that Kansas Secretary of State Kris Kobach pushing the Commerce Department to make the change, in messages citing Kobach’s conversations with then-White House advisor Steve Bannon.

Ross has claimed that he added the citizenship question to help the Department of Justice enforce the Voting Rights Act, but U.S. District Judge Jesse Furman said the secretary’s shifting explanation suggest that this is a pretext.

“In a June 21, 2018 supplement to the administrative record, Secretary Ross admitted that he ‘began considering’ whether to add the citizenship question ‘soon after’ his appointment as secretary in February 2017 — almost ten months before the ‘request’ from DOJ — and that, ‘as part of that deliberative process,’ he and his staff asked the Department of Justice if it ‘would support, and if so would request, inclusion of a citizenship question,’” Furman wrote in a July ruling.

In a memo filed late Thursday night, the Commerce Department noted that the attorneys general face a high bar to make Ross testify.

“The Second Circuit, like its sister circuits, has held that ‘high-ranking government officials are generally shielded from depositions,’ and a departure from this principle may be tolerated only where a plaintiff ‘demonstrate[s] exceptional circumstances,’” the agency’s letter states.

“This hurdle is exceptionally high when plaintiffs seek to compel testimony from a member of the president’s cabinet, one of the highest-ranking government officials, which would ‘have serious repercussions for the relationship between two co-equal branches of government,’” it continues.

Furman, who previously rejected an attempt to force Kobach to testify, has given the citizenship question challengers another opportunity to persuade him to compel testimony from Ross. Their reply brief is due on Tuesday.

If the judge orders Ross to testify, the secretary’s deposition will take place before the end of discovery Oct. 12.

Furman today set a tentative trial date for Nov. 5. The government will have another opportunity after that date to boot the case on summary judgment, but Furman said that he was “skeptical” such a bid would be successful based on evidence that already entered the record.