By Michael Wines, New York Times–

The fight between Congress and President Trump over census documents revolves around one crucial issue: discerning the true motive of the Trump administration when it made a historic decision to ask all residents in the country if they were an American citizen.

Commerce Secretary Wilbur Ross, who oversees the Census Bureau, has long claimed that the government needs more accurate data on citizenship to enforce the Voting Rights Act of 1965. But a growing body of evidence — unearthed in lawsuits seeking to block the question — suggests that the administration added the question to entrench Republicans in power.

Federal judges in three lawsuits have concluded that the Trump administration’s rationale for adding the question was contrived.

Judge Jesse M. Furman of the United States District Court in Manhattan, for instance, criticized Mr. Ross and his aides for giving false or misleading statements under oath as they struggled to explain their rationale.

The Commerce Department’s handling of the question, Judge Furman wrote in his decision, made it clear “that the goal of Secretary Ross and his aides was to launder their request through another agency — that is, to obtain cover for a decision they had already made.” In 54 years of Voting Rights Act enforcement, he noted, the Justice Department had “never before claimed that it had been hampered in any way” by a lack of detailed information on citizenship.

And this month, documents found on the computer backups of a deceased Republican strategist offered the most persuasive evidence yet that the decision was driven not by policy, but by partisanship.

The files show that the strategist, Thomas B. Hofeller, had outlined in 2015 how Republicans could gain political power by basing new political maps on the number of voting-age citizens instead of total population — a strategy, he wrote, that could only be realized with data from a census citizenship question.

Democrats in Congress are seeking to unearth even more information about how the Commerce Department made its decision. Thousands of documents have already been turned up in lawsuits, but almost nothing is known about the extent to which the White House was directly involved.

After Mr. Trump invoked executive privilege to block disclosure of documents on the census, a House committee voted on Wednesday to recommend that the House hold Attorney General William P. Barr and Mr. Ross in contempt of Congress.

Challenges to the citizenship question are now before the Supreme Court, which is expected to issue a final ruling before the court’s term ends later this month. In arguments before the court in April, conservative justices seemed ready to accept the Trump administration’s argument that it had both the discretion and a sound reason to measure citizenship in 2020.

Late Wednesday, plaintiffs in the main census lawsuit asked the Supreme Court to allow further discovery of any remaining evidence in Mr. Hofeller’s backup drives before it issues a ruling in the case.

Experts say that adding a citizenship question would deter immigrants and minority residents from responding to the census, leading to an undercount in the predominantly Democratic areas where the bulk of them live. In addition, a census that reveals with precision where noncitizens live is crucial to plans by some conservatives to base political districts not on total population, but on the number of voting-age citizens. That, too, would benefit Republicans, particularly in states like Texas and California with large numbers of foreign-born residents.

Suspicions that an ulterior motive lay beneath Mr. Ross’s decision have been further bolstered by the way that decision was made — almost totally in secret and without testing of its language, in contrast to the years of surveys and consultation that have preceded every previous change in the census questionnaire.

Terri Ann Lowenthal, a consultant on census matters who managed the issue for the Obama transition team in 2008, said that virtually everything about the administration’s handling of the citizenship question “raised significant alarm bells.”

“The traditional process for determining census questions is done primarily in the public arena,” she said. “And that simply did not happen this time.”

When Mr. Ross announced his decision to add a question on citizenship to the census, he cast it as the culmination of months of intensive research by Census Bureau experts and advice from members of Congress, businesses and interest groups with a stake in an accurate head count and the public.

That was true only in the narrowest of senses. Evidence in the lawsuits shows that interest in the question dated to the fall of 2016, when a transition team preparing for the Trump presidency added it to a list of issues to consider. That suggestion came from Mr. Hofeller, the mastermind of a string of gerrymanders drawn in 2011 that locked the Republican Party into a decade of control in state legislatures nationwide.

Mr. Ross has repeatedly said that he decided to add a citizenship question only after the Justice Department requested it, saying better citizenship data would assist Voting Rights Act enforcement. Evidence in the lawsuits has showed, though, that Mr. Ross pressured the department to request the citizenship question, not the other way around.

Adding the question appeared to be a top priority for the commerce secretary.

Less than two weeks after taking office in 2017, Mr. Ross tasked an aide with researching whether recent censuses had asked about citizenship (they had not) and whether noncitizens were included in population counts used for redistricting (they were).

That April, at the request of Mr. Trump’s chief strategist, Stephen K. Bannon, Mr. Ross talked about the census with Kris Kobach, at the time the Kansas secretary of state and a virulent opponent of immigration. In a subsequent email, Mr. Kobach told Mr. Ross that adding a citizenship question was essential to solve “the problem that aliens who do not actually ‘reside’ in the United States are still counted for congressional apportionment.”

Mr. Ross later said he did not act on Mr. Kobach’s advice.

It was not until December that the Justice Department formally requested a citizenship question in a three-page request saying that adding the query was “critical” to getting precise enough data on noncitizens to enforce the Voting Rights Act.

In the months that followed, expert analysts there concluded that the question would deter at least 630,000 households with millions of residents from filling out the census form, and offered Mr. Ross alternatives that they said would produce much the same data. Both public comments on the proposal and the response from businesses and experts were almost uniformly opposed to adding the question.

Mr. Ross, however, was undeterred, and the Commerce Department later said that his wooing of the Justice Department was not evidence of skulduggery, but a civics-book example of how policy is made.

“Executive branch officials discussing important issues prior to formulating policy is evidence of good government,” a spokesman, Kevin Manning, said in a statement. “Executive branch officials worked together to ensure that Secretary Ross received all of the information necessary to make an informed decision.”

Sheelagh McNeill contributed research in New York