Washington (CNN) Mounting evidence suggests the push to add a citizenship question to the 2020 census began as little more than a political power grab by Republicans.

There were the secret files from now-deceased political strategist Thomas Hofeller, outlining how adding a citizenship question would yield political districts beneficial to Republicans.

There were the poorly hidden conversations between Commerce Secretary Wilbur Ross and anti-immigration hard-liners like former Attorney General Jeff Sessions, former White House chief strategist Steve Bannon and former Kansas Secretary of State Kris Kobach

And then there was the pitch that Kobach -- also known for peddling conspiracy theories about birtherism and voter fraud -- made directly to President Donald Trump and his top aides soon after the inauguration.

With the Supreme Court set to decide whether to allow the citizenship question on the 2020 census -- a ruling with deep ramifications for political clout and the fate of hundreds of billions of dollars in federal funding -- none of this secretive political lobbying could end up mattering much to the high court.

In oral arguments, the conservative justices who hold the majority on the Supreme Court appeared more interested in whether the Commerce secretary had the authority to add the question than whether it was politically motivated.

Once a decade, the census is conducted to tally the entire US population. That data helps the government decide how to distribute federal funds for programs like free and reduced-price school lunches, highway spending and Medicaid.

But the census count is also politically powerful. It determines how many congressional seats each state gets. And it guides lawmakers in drawing the boundaries for congressional and state legislative districts, a process known as redistricting.

When Ross announced in March 2018 that he planned to add the question -- "Is this person a citizen of the United States?" -- to the 2020 census, it set off a year of legal battles. Along the way, documents that became public through congressional inquiries and court proceedings cast doubt on Ross's true intention behind adding the citizenship question.

Discussions with Bannon and White House

In congressional testimony, Ross said the Justice Department asked the Commerce Department to add the question so it could better enforce the Voting Rights Act and protect minority voting rights.

"We are responding solely to the Department of Justice's request, not to any campaign request, not to any other political party request," Ross told Congress in March 2018.

He left out some details. Like the fact that Ross and his team pressed the Justice Department to make that request, according to a court filing.

When Ross was asked during a congressional hearing whether he had any conversations about the citizenship question with Trump or anyone in the White House, Ross replied, "I'm not aware of any such."

That claim hasn't held up either. Court filings show Ross discussed the citizenship issue some of the loudest anti-immigrant voices in the GOP -- some serving in the Trump administration and others advising it from the outside.

Ross spoke to Sessions, then the attorney general, about the citizenship question in the spring of 2017 and multiple times thereafter, according to a court filing. Around that same time, Ross also spoke to Bannon. Bannon asked Ross to speak with Kobach about the citizenship issue, the filing shows.

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Kobach followed up in July 2017, emailing Ross to explain that the citizenship question was necessary because "aliens who do not actually 'reside' in the United States are still counted for congressional apportionment purposes."

By then, Kobach had already pitched Trump on the idea directly. He told the House Oversight Committee that soon after the inauguration, "I did meet with the President and this issue was a subject during a meeting with the President."

Kobach refused to tell the committee whether he had any additional meetings with Trump about the census question. Kobach's lawyer told the committee, "The White House has asserted a complete privilege over those issues."

The Hofeller files

The latest twist in the census drama comes from Hofeller's private files. Hofeller, a GOP political strategist, was regarded as an expert in the art of redistricting, particularly to benefit the Republican Party.

After he died, his estranged daughter uncovered her father's unpublished 2015 study that concluded that asking a citizenship question on the census would provide data to justify redrawing Congressional districts in a way that "would be advantageous to Republicans and non-Hispanic whites."

Court filings show that some of Hofeller's work on this issue made its way into the Justice Department's citizenship request -- some of it word-for-word. The Justice Department has denied the link.

Earlier this month, the American Civil Liberties Union asked the Supreme Court to delay its decision on the citizenship question so a lower court could consider the newly unearthed Hofeller files. In a fiery response, the Justice Department told the court it should not delay one of the most significant cases of the term because of "meritless" and "supposedly new" allegations that the citizenship question was politically motivated.

Solicitor General Noel Francisco said, "there is no basis to conclude that anything Hofeller wrote" influenced the ultimate decision.

Even before the Hofeller files were uncovered, three federal courts ruled that the citizenship question could not be added. A federal judge in New York concluded that the Commerce Secretary "announced his decision in a manner that concealed its true basis."

That hasn't stopped conservatives, including Trump, from championing the citizenship push.

"I think it's totally ridiculous that we would have a census without asking," Trump told reporters earlier this month. "I think when the census goes out, you should find out whether or not -- and you have the right to ask whether or not -- somebody is a citizen of the United States."

Meanwhile, opposition has sprung up from civil rights groups that say, contrary to the administration's claim, this question will actually lead to more minority households going uncounted in the next census. Democratic-led states that stand to lose political representation have opposed it. And data experts, including former census directors, have slammed the move.

"This is clearly done as a political ploy," said William Frey, a Census expert and senior fellow of the Metropolitan Policy Program at the Brookings Institution think tank. "Just because you're not counting those people doesn't mean they're not here."

The Census Bureau's own chief scientist, John Abowd, raised concerns in a memo that concluded adding the citizenship question "is very costly, harms the quality of the Census count, and would use substantially less accurate citizenship status data than are available from administrative sources."

Roughly 22 million people living in the US are non-citizens, according to the Kaiser Family Foundation, and data experts say at least half of those people are here legally.

Still, experts believe noncitizen households, immigrants and Latinos will all be less likely to complete the form, largely out of fear of how that information will be used, experts say.

By the Census Bureau's own estimates, about 6.5 million people would go uncounted.

That means the states they reside in will take a hit, both in terms of political clout and government resources. Among the states that stand to be most impacted are California, Texas, Nevada, New York and New Jersey, according to the Brookings Institution.

"If the Supreme Court decides to allow the citizenship question through and appear on the 2020 census, the effects are going to be cataclysmic for the country," said Thomas Wolf, a census expert and counsel for the Democracy Program at the Brennan Center for Justice. The change will impact "very basic staples of life like education, medical care, and food. Funding for all of those things will ramp down in any state where an undercount occurs."

While the political jockeying behind the citizenship question may ultimately prove irrelevant to the Supreme Court, that hasn't stopped Democrats on Capitol Hill from digging.

After the Trump administration refused congressional demands for more documents about the decision to add the question, the Democrat-led House Oversight Committee voted to hold Attorney General William Barr and Ross in contempt of Congress.

For his part, Ross said in a statement he has been cooperative with the committee, adding, "The Democrats have continued to attack this Administration on dubious grounds, and they aren't going to let the facts get in the way of their own concocted stories."

The contempt vote was also panned by Republicans, who argued citizenship is a common sense question, and note that a similar question was asked on the 1950 census form.

"The only people who don't want to ask the question -- Democrats around the country do, Republicans around the country do, independents around the country do -- the only ones who don't want to ask the question: Democrats in Washington," said Ohio Rep. Jim Jordan, the top Republican on the committee. "Everyone else knows it needs to be asked."