“By design the US Constitution apportions congressional representation by population.”
By design the US Constitution originally apportioned congressional representation by population.
But Amendment XIV changed apportionment from population (with slaves being discounted by 40%) to resident citizens of each state:
“Section 1. All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the state wherein they reside...
“Section 2. Representatives shall be apportioned among the several States according to their respective numbers, counting the whole number of persons in each State, excluding Indians not taxed.”
If the authors of Amendment XIV wanted to retain the original population basis, but end the discounting of blacks, they could have had Section 2 as Section 1 and Section 1 as Section 2.
The 14th did no such ting.
“Section 2. Representatives shall be apportioned among the several States according to their respective numbers, counting the whole number of persons in each State, excluding Indians not taxed.”
Apportionment is not based on citizenship unless a state restricts males from voting. The census counts population “whole number of persons” which is used for apportionment.