If you changed your domicile (your permanent home) from CA to WA this year, then for 2020 you have to file a part-year resident CA tax return. Your income would be taxable by CA until the day you began living in your new domicile in WA. (You became a resident of WA - and a non-resident of CA - on the day you began living in your new domicile in WA).
Once you became a WA resident, only your earnings from work actually (physically) performed inside CA would be taxable by CA. Earnings from work done remotely from a WA location would not be taxable by CA. (There is an exception if you are paid as an independent contractor rather than a W-2 employee.)
Your state tax obligations are NOT determined by your voter registration. They are determined by your state of domicile and (with a few exceptions*) by the location where you actually work.
*A handful of states tax non-resident remote workers, but CA is not one of them as long as you are a W-2 employee.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
