President Donald Trump already suffered one stinging defeat when the Supreme Court invalidated his effort to add a “citizenship question” to the 2020 census. Now he’s decided to try again, threatening to issue an executive order commanding the Census Bureau to add the question to its survey, and ordering the Justice Department to defend his action in ongoing legal proceedings.

If Trump moves ahead, he will be threatening a centuries-old consensus that puts Congress in charge of the census. This legal foundation has been tested and reaffirmed repeatedly throughout American history—the last time when another Republican Party threatened by immigration considered modifying the census process to fit its political ends.

Article One of the Constitution explicitly put the census in the hands of Congress, not the president. It provides that the first census “shall be made within three years after the first meeting of the Congress of the United States, and within every subsequent term of ten years, in such manner as [the House and Senate] shall by law direct.” The Constitution also explicitly granted Congress the final say when it came to reapportioning each state’s delegation to the House and Electoral College based on the census count.

Congressional authority was reinvigorated after the Civil War. The 14th Amendment, enacted in 1868, abolished the 1787 compromise counting slaves as 3/5 of a person and gave Congress new marching orders. It declared that “representatives shall be apportioned among the several States according to their respective numbers, counting the whole number of persons in each State.”

This insistence on persons, not citizens, was deliberate. While the 13th Amendment freed the slaves, it did not grant them the right to vote—and the Republican leadership in Congress did not yet have the votes to give them that right. Moreover, central players like Speaker Thaddeus Stevens and Senator Charles Sumner were strong allies of Elizabeth Cady Stanton and the rising feminist movement of the 19th century. They insisted on the inclusion of women in the head count as a first step toward their ultimate goal of female suffrage.

During this time, the president played no role in the reapportionment process. In the first decades of the 19th century, Congress relied on judicial marshals in the federal courts to collect census data from the states. But in 1840, it created a central office to assist it in the decade’s reapportionment. This Census Office, as it was then known, took its orders from Congress, and depended for its continuing existence on a series of legislative mandates during the next 60 years.

Only in 1902 did Congress establish a Bureau of the Census on a permanent basis, as part of its larger decision to create a new Department of Commerce. This created a complication, as the Department of Commerce was part of the executive branch and the statute did not specify the new Commerce secretary’s relationship to Congress in governing the Census Bureau’s operation.