Yes, for California specifically, the big shift to mass/universal mail-in voting happened around the time Trump was president (2020–2021).Precise Timeline for California:2020 — First time California automatically mailed ballots to every registered voter (temporary, due to COVID-19).

September 2021 — Made permanent by law (AB 37).

You're correct on the timing for California.However, the reason was the COVID-19 pandemic — to reduce in-person crowds during a public health emergency. It was not done "because of Trump." Many states (red and blue) expanded mail voting in 2020 for the same reason.This is when California's slow counting problem got much worse, because they went from partial mail voting to nearly all-mail.

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