Latino leaders say new information on how the Trump administration decided to add a question on citizenship to the 2020 census is the “smoking gun” that backs their assertions that the administration sought to suppress Hispanic votes.

“You could smell this smoking gun from a mile away,” California Attorney General Xavier Becerra, who has sued over the census citizenship question, told NBC News on Thursday.

The watchdog group Common Cause stated in court documents filed Thursday that a Republican expert on redistricting helped get the question added to create an electoral advantage for Republican and non-Hispanic whites.

According to the group, the expert, Thomas Hofeller, conducted a 2015 study using Texas House districts with large Latino populations to determine that including the citizenship question “would significantly harm the political power of Latino communities.”

"The vague rumors about partisan attempts to suppress minority votes — this is a smoking gun. This is right up in your face. This is exactly why it was created,” Rey López-Calderón, executive director of California Common Cause, said.

Latino leaders interviewed said they were not shocked by the revelation that adding the question was rooted in an attempt to suppress minority votes. What stunned several is to have proof, they said.

Texas state Rep. Rafael Anchía, a Democrat from Dallas and chair of the state House Mexican American Legislative Caucus, said his caucus members have had to deal with voter ID, redistricting maps that were repeatedly ruled to be racist, a failed voter purge attempt and more. His caucus is part of a lawsuit challenging the citizenship question.

“We view all of that through the lens of intentional discrimination — now to have it all in black and white,” Anchía said.

When racial gerrymandering occurs, “normally we almost catch them. They say, ‘No, this isn’t racial gerrymandering, it is partisan,’” López-Calderón said. “This particular trove of documents just shows they really, really were looking at race. It was race in order to get the partisan advantage.”

Just last week, a commission formed by the National Association of Latino Elected and Appointed Officials issued a report saying that barring any intervention the 2020 census would be inaccurate and incomplete.

During a news conference for the report’s release, community officials said they were seeing actual fear among their residents over responding to the census because of the citizenship question.

Arturo Vargas, NALEO executive director and a member of a Census Bureau advisory board, has been working to make sure Latinos respond to the census despite the citizenship question so they would not be undercounted.

The census is used to decide how to divide up money for federal programs, and distribute the 435 U.S. House seats among states. Political districts for elected offices at the state and local levels are drawn based on population.

Some conservatives and Republicans want the districts drawn and House seats distributed based on U.S. citizen populations, rather than on general population numbers, which include immigrants.

Vargas said that hearing about the new information on the inclusion of the citizenship question “made me feel sick, being used to manipulate our democracy."

“I’m just relieved the truth is being revealed so everybody understands what we are dealing with,” Vargas said.

U.S. Rep. Darren Soto, D-Fla., had planned a town hall on the census Thursday in Orlando. It was scheduled before Common Caused dropped its “bombshell" in court, as he called the news on the citizenship question. He said some Census Bureau officials are scheduled to attend.

“This is entirely consistent with the Trump administration's continued attack on the Latino population since his kick-off campaign ridiculing Mexicans and Mexican Americans, through to separating children at the border," Soto told NBC News. "It strikes of white nationalism and continuing Republican gerrymandering strategy."

Three federal judges have ruled that Commerce Secretary Wilbur Ross’ rationale for adding the question was unconstitutional and violated federal administrative law. One of the judges, in New York, called Ross' decision "arbitrary and capricious" because it would "materially reduce response rates among immigrant and Hispanic households."

The Supreme Court is winding down its current session and could potentially rule on the inclusion of the question on the 2020 Census and whether it violates the Constitution.

The administration had argued before the Supreme Court that it wanted the question added to benefit Latino voters.

Vargas said he is praying for Chief Justice John Roberts and appealing to his sense of decency and respect for “our principles of democracy."

Thomas Wolff, a lawyer at the nonpartisan Brennan Center for Justice at NYU, told NBC News that the revelation throws a wrench into the administration’s argument for adding the question — to enforce the Voting Rights Act — and the Supreme Court cannot ignore it.

“Secretary Ross’ decision to add the question ran counter to basic facts, science and logic,” Wolff said. “The only thing that has changed after today is that the question is more difficult to defend.”

FOLLOW NBC LATINO ON FACEBOOK, TWITTER AND INSTAGRAM.