The United States Constitution requires that a census be conducted every ten years (Article I, Section 2, Clause 3). Under the Supreme Court decision in Baker vs. Carr, the one man-one vote mandate was established which required that each federal Congressional district be of roughly equal population. Since the number of representatives is legislatively established at 435 and since the US population is about 330 million, that means that each Congressional district be composed of roughly 759,000 people.
But, let’s step back and look at the reason for the census. The purpose is not necessarily to determine how much money a state gets in federal highway, healthcare, education, or any other funds. These are much later outgrowths of the use of the census and not its original purpose. The original enumerated purpose was to determine how many representatives in Congress a state gets with each state guaranteed at least one regardless of population. This was done with an eye towards obvious population shifts within the United States, and as new states were added and populated. Hence, despite all these new reasons given for the census, its primary purpose is reapportionment of representatives between the states. Baker vs. Carr goes further and dives into the individual states and mandates, in a broad outline, how Congressional districts are to be drawn- roughly equal population.
Of course, there have been other intervening factors, the most important of which is the Voting Rights Act of 1965 which was designed to give minorities greater access to voting rights and representation. Some states have also passed laws that place restrictions on how Congressional district lines are drawn. For example, a state may require that contiguous counties be included in a single district.
Since the purpose of the census is for enumeration purposes for the House of Representatives and since only citizens of the United States and their individual states are legally permitted to vote in elections, it would make intuitive sense that only U.S. citizens be counted in the census for this purpose. Theoretically, one can use a bifurcated system for use of the census: citizens only for enumeration purposes, and overall population for all other purposes.
There is historical precedence for such a scenario right there in the Constitution. The same Constitutional Clause that establishes the census specifically excludes “Indians not taxed,” and two-fifths of “all other persons,” the so-called and oft-misunderstood “three-fifths compromise.” Hence, for apportionment purposes it makes sense to include only United States citizens as defined by law and the United States Constitution.
People have forgotten the underlying purpose of the census and now concentrate on the funding, or revenue-sharing, aspect of its use. Requiring that Congressional districts be redrawn or apportioned among the states does not upset those requirements, if codified, in a bifurcated use of the census. For example, according to recent (2018) estimates, only two states- California and Texas- have a population that falls below 90% US citizens. Let’s use California as an example with an estimated population of 39.5 million. For reapportionment purposes, based on those recent estimates, 13% of the population are not US citizens. Hence, we subtract out that 13%, or about 5.136 million people leaving 34.375 million citizens.
Although they may lose representatives in Congress and districts necessarily made larger in some cases, the amount of federal funds flowing to California would be based on total population. Further, since that money does not flow necessarily to a district but to the state coffers, it is up to the state government to disburse those funds as they see fit. The state would be under no mandate to change their state legislative district boundaries and could use total population rather than citizen population for those purposes. That is, only the number of representatives a state has and the size of the resulting districts would be affected. Furthermore, under this scenario, each Representative would represent 701,000 US citizens rather than 759,000 people.
In effect, such a system would be defining, for Federal apportionment purposes, the “man” in Baker vs. Carr as United States citizens. Since that case was based on the Fourteenth Amendment’s Equal Protection Clause in the guise of voting rights, how the “voting rights” of someone ineligible to vote in the first place would be infringed would strain the boundaries of logic. Would the non-citizen ineligible to vote lose “representation?” Possibly, although that is hard to understand why: they live in a district that is “represented.” But where is it written in the Constitution or anywhere else that non-citizens must be “represented?” other than the word “persons” in the Constitution. That word has been used to exclude whole swaths of the population from the more important right to vote, let alone be represented in Congress.
If a state like California wants to use their revenue to give non-citizens in-state tuition or free healthcare, they are free to do so, if allowed. They can do what they want with state revenue. Note that in this bifurcated system, they would lose not a single federal dollar normally due them. That excuse against the system is simply foreclosed. What the state does with those dollars within the parameters of the funding is up to that state. So how would this system affect reapportionment nationally?
Under the proposed system, the following would happen with 435 seats in the House:
Gaining Seats: Arizona +1, Colorado +1, Florida +1, Missouri +1, Montana +1, North Carolina +1, and Texas +1
Losing Seats: California -3, Illinois -1, New Jersey -1, New York -2, and Rhode Island -1.
From this list, one can see the opposition and it has nothing to do with representation in the House or with federal funds. It has everything to do with the Electoral College. Reliably blue states (I am including Colorado) would lose a net seven electoral votes while swing and reliably red states pick up a net seven electoral votes.
That is the true fear that spurs opposition to using citizenship as a basis for reapportionment purposes. Since the census is for representation in the House and since we determine those representatives through voting, then only Constitutionally eligible voters (i.e., US citizens) and their progeny (children)- regardless of registration, voting history, state laws, or other factors- should be used for apportionment purposes. The ex-felon, the child or adolescent, or the non-voter may not be allowed to vote or may not be legally eligible to vote or just choose not to vote, but by virtue of their US citizenship, they are counted in the census for these apportionment purposes.