New York Attorney General Barbara Underwood is asking a federal judge to compel U.S. Commerce Secretary Wilbur Ross to appear for a deposition as part of her lawsuit over his agency's decision to ask about citizenship on the national census in 2020.

In a filing late Monday, Underwood's office said the Trump administration has so far been unwilling to make Ross available for a deposition and that information potentially gleaned from his testimony cannot be obtained elsewhere.

The case is before U.S. District Judge Jesse Furman of the Southern District of New York.

Executive Deputy Attorney General Matthew Colangelo wrote in Monday's filing that three other officials at the Commerce Department have already testified that Ross “was privy to unique, firsthand information central to these claims.”

The Commerce Department announced in March that it would be reinstating a question about citizenship to the next census. The U.S. Census Bureau operates under the Commerce Department.

Underwood is leading a coalition of 18 state attorneys general in a lawsuit against the federal agency for adding the question.

They have argued that asking about citizenship will decrease turnout for the census in states with large immigrant populations, like New York. That could have a ripple effect by causing those states to lose representatives in Congress and the Electoral College. The attorneys general also argued that a smaller recorded population could mean less federal funding in areas like education and health care.

A spokesperson for the Commerce Department declined to comment on Underwood's request to depose Ross on Tuesday afternoon, but said they are looking forward to their day in court.

“The department is not going to comment on the specifics of ongoing litigation, but these cases are without merit,” the spokesperson said. “We look forward to prevailing in court and continuing to work with the Census Bureau to conduct a complete and accurate 2020 census.”

Kate Bailey is the lead attorney from the Department of Justice representing the Trump administration.

Three senior advisors at the Commerce Department were already deposed last month over the citizenship question, according to filings. Those were chief of staff at the Commerce Department Wendy Teramoto, acting deputy secretary Karen Dunn Kelley and Earl Comstock, policy director and deputy chief of staff at the agency.

Teramoto told attorneys in her deposition several times that she could not speak to Ross' conversations with the Department of Justice about the citizenship question. She told attorneys they would have to speak with Ross himself for answers about his communications with the DOJ.

Comstock, in his deposition, said the same about a memo in which Ross said other administration officials had previously brought up the idea of adding the citizenship question in the early months of President Donald Trump's presidency. Comstock said he did not know which officials Ross was speaking about and directed attorneys to ask Ross himself.

Their depositions provided few answers to where the conversation about adding the citizenship question started and how exactly it came about. That's why the attorneys general want to depose Ross, Colangelo said in the filing. He is one of few officials that would have direct knowledge of the situation.

“Aside from [Ross], there is no other source who can testify regarding his thought processes, key conversations that informed or reflected those thought processes, and subsequent actions,” Colangelo said.

They are seeking to identify the other administration officials involved in adding the citizenship question who have so far gone unnamed.

Colangelo said the Trump administration has instead suggested the states request written discovery rather than a deposition from Ross. He said a deposition would be ideal because similar requests during the discovery process have so far been returned incomplete.

The attorneys general were scheduled to depose acting assistant attorney general for civil rights John Gore this week in the case, but that deposition was stayed by the Second Circuit pending the determination for a petition of writs of mandamus over discovery sought from DOJ.

Gore allegedly ghostwrote a letter from the DOJ to Ross asking that the citizenship question be added to the census, Furman said in a previous decision.

A status conference in the case is scheduled for Friday afternoon.

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