The Trump administration pushed for the citizenship question in the census to enable legislators to draw electoral districts based on eligible voters. This is allowed by the constitution and some states have shown an interest in it.
The U.S. Supreme Court unanimously stated in its April, 2016 Evenwel v. Abbott ruling that legislative districts may, but do not have to be drawn inclusive of all the people living within them, as has been the standard for at least the past five decades.
Justice Ginsburg wrote in the opinion, “Nonvoters have an important stake in many policy debates—children, their parents, even their grandparents, for example, have a stake in a strong public-education system—and in receiving constituent services, such as help navigating public-benefits bureaucracies. By ensuring that each representative is subject to requests and suggestions from the same number of constituents, total population apportionment promotes equitable and effective representation.”
But as Justices Samuel Alito and Clarence Thomas pointed out in their own separate written opinions, the Evenwel decision still allows for states to pass voter-only or citizen-only districting designs.
In December, 2015, Harvard political science professor Carl E. Klarner found that “utilizing [voting age population] for districting would result in a 12% reduction in Latino state legislators and a 13% reduction in Latino U.S. Representatives,” and that “Latino voting power in the mass public would decline by 4.6% in the U.S. House, 5.2% in state senates and 6.2% in state houses.”
A July 12, 2019 article in the New Yorker covers the Thomas Hofeller story and the Trump Administration’s effort to put a citizenship question into the census. It quotes Trump saying “ “Some states may want to draw state and local legislative districts, based upon the voter eligible population.”
According to the AP, “The concept [of using only voter-eligible populations] was introduced in legislation over the last few years in Missouri and Nebraska, where the state constitution already calls for excluding “aliens” from its apportionment.
In Texas, Hofeller calculated in his report that about a half-dozen Latino-dominated districts would disappear, including a portion of one in the Dallas area, up to two in Houston’s Harris County and two or three in the border counties of South Texas.”