It went largely unnoticed last week, but the Trump administration’s ongoing campaign to structurally tilt American democracy in the Republican Party’s favor is proceeding apace. President Donald Trump ordered the Census Bureau to compile citizenship data from existing federal records last month, after the Supreme Court effectively blocked a citizenship question on the census itself. In a letter to Massachusetts Representative Ayanna Pressley, the bureau confirmed it would produce that data in a highly auspicious form.

“Administrative records will use existing government information to produce citizen voting age population (CVAP) data at the census block level, the smallest geographic data unit,” the bureau told Pressley’s office last week. “The block-level data will have the same strong privacy safeguards used for the 2020 Census. The Census Bureau cannot and will not share individual respondent information with any other government or non-government entity, including law enforcement.”

While not obvious at first blush, this arcane minutiae carries massive consequences for American politics. Every ten years, state legislatures redraw both their own seats and federal House districts using the bureau’s block-level data on total population—the Census-tabulated head count of every single person inside the United States. By also providing block-level data on eligible voters, the bureau is opening the door for states to redraw their legislative maps in 2021 based on that population base instead.

Such a move would reshape the political and social topography of any state that tries it. Legislative seats—and the raw political power that comes with them—would shift away from diverse urban areas and gravitate toward whiter suburban and rural communities. The centers of political gravity would also bend in those directions, resulting in state legislative maps that strongly favor the Republican Party. The effects of extreme partisan gerrymandering and stringent voter-ID laws would be amplified.

It’s no secret that Republicans are considering this option; this precise outcome has been the sought-after result of the Trump administration’s intrusions into Census policy. In 2016, a host of conservative legal groups urged the Supreme Court to rule that using total population to draw districts violated the “one-person, one-vote” rule. Texas state officials took the opposite view in its own defense, but with a twist: They told the justices that it would be permissible for Texas to use any reliable population base when drawing districts, whether it be total population, eligible voters, or something else. The court declined to answer that question and simply ruled that the use of total population is constitutional.