You do not need disenfranchisement, just apathetic voters who do not currently contribute. Right now there are ~23 million voters registered in California. 45% registered D, 25 %R, giving absolute numbers of 10 million D, and ~6 million R. Which you can handwave is 4 million Ds who know they do not need to contribute - their neighbor has their back to secure the state electoral votes.

Looking at the US as a whole, there are 44 million registered D with 37 million R. If you could round up all affiliated voters, Dems win the presidency every election if going by popular vote[0].

[0] https://usafacts.org/articles/how-many-voters-have-a-party-a...