Hansi Lo Wang for NPR:

President Trump releaseda memorandum Tuesday that calls for an unprecedented change to the constitutionally mandated count of every person living in the country — the exclusion of unauthorized immigrants from the numbers used to divide up seats in Congress among the states.

The memo instructs Commerce Secretary Wilbur Ross, who oversees the Commerce Department, to include in the legally required report of census results to the president “information permitting the President, to the extent practicable” to leave out the number of immigrants living in the U.S. without authorization from the apportionment count.

But the move by the president, who does not have final authority over the census, is more likely to spur legal challenges and political spectacle in the last months before this year’s presidential election than a transformation of the once-a-decade head count.

Since the first U.S. census in 1790, both U.S. citizens and noncitizens — regardless of immigration status — have been included in the country’s official population counts.

The fifth sentence of the Constitution specifies that “persons” residing in the states should be counted every 10 years to determine each state’s share of seats in the House of Representatives. The 14th Amendment goes further to require the counting of the “whole number of persons in each state.”

It is Congress — not the president — that Article 1, Section 2 of the country’s founding document empowers to carry out the “actual enumeration” of the country’s population in “such manner as they shall by law direct.”

In Title 2 of the U.S. Code, Congress detailed its instructions for the president to report to lawmakers the tally of the “whole number of persons” living in each state for the reapportionment of House seats. In Title 13, Congress established additional key dates for the “tabulation of total population.”