Commerce Secretary Wilbur Ross appears before the House Committee on Oversight and Government Reform in Oct. 2017 to discuss preparing for the 2020 Census. (J. Scott Applewhite/AP)

In the six months since Commerce Secretary Wilbur Ross said he would add a question about citizenship to the 2020 Census, Democratic lawmakers have railed against the move, calling it politically motivated and harmful to the count’s accuracy.

But there hasn’t been much they could do about it.

That could change after the midterm elections next month. If Democrats take the House, the Senate or both, they may wield enough legislative power to block the citizenship question, perhaps by defunding any census form that includes the question. They also vow to probe more deeply into whether Trump administration officials lied about why the question was added.

“If Democrats are fortunate enough to take the majority in November, we will conduct fact-based oversight of these matters, which means obtaining documents and holding hearings to ensure that this Administration is held accountable to the American people,” said Rep. Elijah. E. Cummings (Md.), the top Democrat on the House Oversight and Government Reform Committee, who has been pushing for months for an investigation into the origins of the question.

Critics of Ross’s March 26 announcement, including immigrants’ rights groups and states with large immigrant and minority populations, say adding the question would depress the response rate from immigrant communities, leading to an undercount that could affect congressional redistricting, which is based on the census, as well as the distribution of federal funding. They have also stressed that the U.S. Constitution explicitly mandates an accurate census.

Ross argued that the citizenship question for 2020 is necessary for enforcement of the Voting Rights Act. But six former Census Bureau directors who served under Republican and Democrat administrations have opposed adding the question, which has not undergone the rigorous testing new questions generally go through before being added to the forms.

The controversy only sharpened over the summer when a New York-led lawsuit challenging the question compelled the government to release internal documents around the issue. Those documents indicated that the impetus to add the question came originally from Ross in consultation with former White House senior counselor Stephen K. Bannon, and not from the Department of Justice, as Ross had testified before Congress in the spring.

The documents also included an analysis by the Census Bureau’s chief scientist warning that adding the question would be “very costly, harms the quality of the census count, and would use substantially less accurate citizenship status data than are available” from existing federal records.

So far the most viable avenue for blocking the question has lain in six lawsuits that have challenged it, including the New York one, whose plaintiffs include 18 states plus the District of Columbia and several cities and civic organizations. That is scheduled to go to trial Nov. 5, the day before the midterms.

The Trump administration has made several attempts to block or limit the suit and this week appealed to the Supreme Court to prevent the deposition of Ross, which was scheduled to happen this week; on Tuesday night, Justice Ruth Bader Ginsburg granted a temporary stay. Given the possibility for appeals, litigation could extend into next year, potentially pushing up against next summer when census forms are due to be printed.

So far, Democrats say their requests for documents and subpoenas over the question have been ignored. On Tuesday, , two Democratic congressmen, Cummings and Rep. Gerald E. Connolly (Va.), wrote to the inspector general of the Department of Commerce, asking her to investigate the issue and saying their efforts have “been frustrated by Secretary Ross’ refusal to comply with our oversight requests, the Department of Commerce’s failure to provide documentation due to ‘ongoing litigation,’ and the failure of Republican Committee Members to join our requests to obtain information, documents, or testimony.”

Commerce spokesperson Kevin Manning on Wednesday defended Ross’s original explanation for the question. “Nothing in the tens of thousands of pages of public documents changes the sound rationale he articulated in March,” he said. “These productions reinforce that Secretary Ross received all of the information necessary to make an informed decision after taking a hard look at the question and considering all relevant facts.” The office of the inspector general said it was reviewing the congressmen’s letter.

With control of either chamber, Democrats could look for legislative opportunities to overturn Ross’s decision. One approach would be including language in an appropriations bill that prohibits funding for a census form that includes the citizenship question. This would need to happen in the near future because of the looming deadline for printing the forms.

Control of both houses of Congress would increase the chances that such an effort would be successful. If Democrats win control of the House, they could still wield some influence in the lame duck session over final negotiations on the 2019 fiscal year appropriations bill that covers the Commerce Department and Census Bureau.

If the Senate remains under Republican control, it could be an uphill battle, said Terri Ann Lowenthal, a former staff director of the House census oversight subcommittee. “The administration has been fighting hard against efforts in court to overturn the Secretary’s decision,” she said. But if the effort is wrapped up in a larger bill that covers many programs and initiatives of importance both to the White House and to members of Congress, she said, “It comes down to priorities sometimes, and whether a president or congressional leaders are willing to go to the mat over specific issues and risk a government shutdown, for example, if an appropriations bill doesn’t pass on time.”

Congressman José E. Serrano (D-N.Y.), who has been a vocal critic of the citizenship question, said he would consider “defunding that part, putting in language saying that question would not be included.”

As to possible pushback from the administration, Serrano said, “Let’s see what the mood is then . . . when they hear it from the majority party. Now, all the concerns are coming from the minority party, so they can just ignore them.”

As the ranking Democrat on the committee, Cummings would have subpoena power and the power to call hearings and investigations, efforts he said have so far been stymied by his Republican counterpart.

“I have asked Chairman (Trey) Gowdy to obtain documents from the Commerce Department and the Justice Department, but he has declined,” Cummings said in an email. “I have also asked Chairman Gowdy to hold a hearing to have Secretary Ross explain the misleading testimony that was given to our committee and several others, but the Chairman has refused.”

Serrano said he is not currently focused on the issue of Ross’s conflicting testimony, though that could come later. “Our primary concern right now is getting rid of the question. How the question ended up there, who supported it, who didn’t, we can deal with that afterward. As to whether he lied to us, that’s very important. But we have to use all our energy right now on this to get rid of the question.”

But Sen. Brian Schatz (D-Hawaii), a critic of the citizenship question, said legislation to eliminate it may not be necessary. “I think we have to win in court and I’m confident that we will,” he said. “We don’t need a new law. We have the Constitution on our side. We just need to ensure that they comply with the constitution.”

But if time runs out, he said, “then we’ll consider emergency legislation.”

The 2020 count was beset by problems even before the citizenship question arose. Its director resigned in May 2017 around questions of funding. Insufficient funding forced the bureau to cancel two out of three planned field tests, and critics say new cost-saving digital approaches have not been adequately tested or protected from cybersecurity threats. The company contracted to print the forms went bankrupt and the government must now find a new one; a U.S. Government Publishing Office spokesperson said a new contract should be awarded in November.

As to what the bureau will do if the question is not resolved by the time the forms need to be printed, bureau spokesman Michael C. Cook Sr. said, “The U.S. Census Bureau routinely creates and updates its contingency plans as needed,” and added that more details would be forthcoming once the new contract is awarded.

At a hearing earlier this month for Census Bureau director nominee Steven Dillingham, senators from both sides of the aisle grilled him on his views of the citizenship question; he declined to state an opinion, saying he would follow the ruling of the courts.

The Trump administration had earlier considered Thomas Brunell, a political science professor best known for his work on behalf of Republican redistricting plans and a book that argues against competitive electoral districts, sparking fears of partisan influence over the census.

Dillingham, who has led smaller federal statistical agencies, including the Bureau of Justice Statistics and the Bureau of Transportation Statistics, has not faced the same kind of criticism.

“The new director is by all accounts a good choice and has the professional background and the credibility to make sure that we count everybody in America,” Schatz said. “So far he looks like a pro.”

As to whether the ascension last week of Brett M. Kavanaugh to the Supreme Court might make it harder for litigants, Schatz said, “I think this is not a close call legally. They are in clear violation of the administrative procedures act and the Constitution . . . it’s not an open question.”

Robert Barnes contributed to this report.