If you look at the tax situation across the states, the party split makes a bit more sense. Of the states involved in the pilot program, Florida, Nevada, South Dakota, Tennessee, Texas, and (to some extent) Washington do not have individual income tax. Also, Arizona and New Hampshire both have a flat rate income tax, which I readily admit knowing nothing about, but which I presume simplifies them being part of the pilot. So California, Massachusetts, and New York are the only states which have a variable tax rate and also opted in, and are also all about as Democrat leaning as it gets.

https://taxfoundation.org/data/all/state/state-income-tax-ra...