If Apportionment was based on Registered Voters

[jimrtex]

The Texas Constitution says that Senate districts are to be based on the number of qualified voters, but this is ignored since no one knows a practical way to determine the number of qualified voters.

It should be noted that there is no requirement of citizenship in order to vote, and up until the early 1900s many states permitted legal permanent residents to vote.  On the frontier, this was a practical matter since the organization of state and local governments was often based on having a certain number of voters.

[jimrtex]

Though I don't get this to quite add up, it seems to me that right now there would be next to no partisan change. So why not?

It would require a Constitutional Amendment.

When one of the precursors to the 14th Amendment was debated, there was suggestions that apportionment be changed to be based on voters (or males over 21).  This would have simplified the penalty for disenfranchisement, since apportionment could be based on the number of adult males who could vote.  In the debate, it was quite obvious that everyone had gone through the census reports to determine what effect that change would have on their state's representation.