Perhaps no institution is more important to the functioning of American democracy than the census, the once-a-decade count of the U.S. population that determines congressional representation — and where billions in federal dollars will be spent. Yet both the GOP-led Congress and the Trump administration have hobbled the 2020 Census effort, which is entering its crucial final stages. Lawmakers have underfunded the Census Bureau, the White House has mismanaged the agency, and now the Justice Department is pushing for a change that could skew the count in Republicans’ favor.

Investigative reporting organization ProPublica disclosed last week that a Justice Department official formally asked the Census Bureau to add a question to the 2020 Census. Adding any question at this stage would be dicey, given that the bureau often runs extensive field tests before fiddling with its forms, ensuring that last-minute changes do not throw off its counting efforts. Worse, the Justice Department requested that the bureau inquire about people’s citizenship status. This threatens to sabotage the 2020 count.

Asking about citizenship status would drive down response rates. Since its inception, the census has not only counted voters; it has taken a precise snapshot of everyone in the country. This helps government agencies to direct scarce dollars, and businesses to guide investment decisions. It is also crucial for doling out congressional representation. As the Supreme Court recently underscored, the Constitution requires that congressional seats be apportioned to states according to their total populations, not only their voting populations. Asking about citizenship status would deter undocumented people — or even legal immigrants who fear how far the Trump administration’s crackdown on foreigners will extend — from returning census forms. Many states — particularly blue states — could end up shortchanged.

The bureau’s charge to count everyone does not change when fewer people fill out their census forms. In that circumstance, the federal government would have to send out census takers to knock on doors and talk to neighbors. Costs would rise substantially, even for a potentially less accurate count. Congress’ shortsighted underfunding of the bureau has, perversely, already resulted in cost overruns, as investments in new techniques and technology were not made. Adding another challenge for the bureau to overcome could require lawmakers to pony up even more last-minute cash to save the count.

Commerce Secretary Wilbur Ross should refuse to add acitizenship status question to the 2020 Census. If he does not, Congress should reject the change.

Editorial by The Washington Post