It’s the same issue that the Supreme Court faced in Reynolds v. Sims — the 1964 case that established “one person, one vote.” It occurs in other countries as well: The British Parliament had to pass the Reform Act of 1832 to remedy the “rotten borough” situation, in which some members of the House of Commons represented thousands of people while others represented literally nobody.
When you cast a vote, you don’t expect that your vote may count for less than someone else’s merely because of where they live. But that’s what Texas is trying to do: The state drew its districts to equalize total populations, ignoring how many of those people are eligible voters. (This is what nearly all states do, though 10 have constitutional or statutory provisions that exclude particular groups — such as foreigners, military personnel and inmates — from districting calculations.) The result is a plan that would create one Senate district with 388,000 eligible voters and another with 611,000. Those in the first district would have votes that count for double the votes of those in the second.
The 14th Amendment’s Equal Protection Clause — “no state shall … deny to any person within its jurisdiction the equal protection of the laws” — doesn’t require absolutely equal districts, but surely ratios approaching 2‐to‐1 go beyond even the constitutional wiggle room allowed by the Reynoldsprecedent. If a state really only has to care about total population, it could theoretically create districts in which only 10 percent, 5 percent or even 1 percent of residents were eligible voters — and those tiny groups of voters would each be able to choose one representative all the same.