A new stash of documents obtained by Congress has confirmed that the Trump administration pushed to add a citizenship question to the census to help Republicans win elections, not to protect people’s voting rights, a House committee report concluded Wednesday.

The report from the Committee on Oversight and Reform, the culmination of a yearslong investigation, detailed new findings based on drafts of internal memos and secret e-mail communications between political appointees at the Commerce Department, which oversees the Census Bureau, and counterparts in the Justice Department.

The documents provided the most definitive evidence yet that the Trump administration aimed to exclude noncitizens from the count to influence congressional apportionment that would benefit the Republican Party, the report concluded, and that senior officials used a false pretext to build a legal case for asking all residents of the United States whether they were American citizens.

Former Commerce Secretary Wilbur Ross had said in congressional testimony that the government decided to add the question because it required more accurate data on citizenship to enforce the Voting Rights Act of 1965. But the Supreme Court in June 2019 ruled that the rationale “appears to have been contrived,” and a week later, the Trump administration abandoned its quest to ask about citizenship in the 2020 census.

Still, a protracted fight between the House committee and former President Donald Trump over the release of a trove of documents that might shed light on the matter stretched to the end of his term. After Trump left office, the committee entered into an agreement with the departments of Commerce and Justice to obtain the previously withheld documents.

“For years, the Trump administration delayed and obstructed the oversight committee’s investigation into the true reason for adding a citizenship question to the 2020 census, even after the Supreme Court ruled the administration’s efforts were illegal,” said Representative Carolyn Maloney, the New York Democrat who chairs the committee.

“Today’s committee memo pulls back the curtain on this shameful conduct and shows clearly how the Trump administration secretly tried to manipulate the census for political gain while lying to the public and Congress about their goals,” she said.

When some internal communications first came to light in 2018, the Commerce Department said that nothing in them contradicted the rationale Ross had earlier offered to Congress.

“Executive branch officials discussing important issues prior to formulating policy is evidence of good government,” a department spokesman, Kevin Manning, said at the time.

The committee was expected on Wednesday to mark up a bill to enhance the institutional independence of the Census Bureau to prevent political interference in the agency.

The report Wednesday cites multiple drafts of an August 2017 memo about the citizenship question prepared by James Uthmeier, a political appointee and lawyer at the Commerce Department, that show him initially expressing skepticism and eventually forceful support for inclusion of the question.

“Over 200 years of precedent, along with substantially convincing historical and textual arguments suggest that citizenship data likely cannot be used for purposes of apportioning representatives,” Uthmeier said in an early memo.

In later drafts, Uthmeier and another political appointee, Earl Comstock, altered or removed language that said that adding a citizenship question was likely to be illegal and unconstitutional, the investigators found.

“Ultimately, we do not make decisions on how the data should be used for apportionment, that is for Congress (or possibly the president) to decide,” Uthmeier said in a later e-mail to Comstock, to which a revised memo was attached.

“I think that’s our hook here,” he wrote.

Officials also added language to emphasize the commerce secretary’s discretion over adding the citizenship question.

The final memo reached the opposite conclusion of the initial draft, asserting that “there is nothing illegal or unconstitutional about adding a citizenship question” and claiming “there are bases for legal arguments that the Founding Fathers intended for the apportionment count to be based on legal inhabitants.”

A handwritten note from Uthmeier to John Gore, a political appointee at the Justice Department, demonstrated that the political appointees had steered the Justice Department to ask the Commerce Department to add the citizenship question, the report said.

The Justice Department ultimately sent a formal request in December 2017 to the Commerce Department requesting that the “critical” information be obtained from households. Ross stated later that, in adding the question to the 2020 census, the agency was fulfilling that request.

Every 10 years, the federal government conducts a census to count all people in the country. Everyone is counted without exception, whether they are adults or children, citizens or noncitizens.

The count is used to allocate funds to federal programs. It also has a significant impact on the nation’s politics, because it is used to apportion representation in Congress, the Electoral College, and within state legislatures.

Adding the citizenship question would have meant asking every member of every household in the country about their citizenship status.

The United States is home to some 22 million people who are not citizens but are in the country legally. Among them are green-card holders, professionals on work visas, and foreign students. About 11 million are living in the country without legal permission.

Experts predicted that the citizenship question would have intimidated immigrants — both legal and those living in the country without legal permission — into shunning the census, resulting in an undercount of several million that would most likely have undermined Democrats by shifting political power from diverse, urban areas to rural ones.

Work at Boston Globe Media