Ok - maybe I’m missing your point completely.
AFAIK, mail-in voting was legal in the 2016, 2020, and will be legal in the 2024 elections. Of course, it varies by state bc there is no big federal group like Elections Canada there.
For the 2020 election, the GOP pushed the narrative that mail-in voting was fraudulent. However, that had the unintended consequence of lowering the potential GOP voting bloc, some of whom would have voted by mail. Realizing that “mail-in voting is bad” narrative is not going to help them in the 2024 election, now they’re saying that it’s fine again.
I’m not sure what the “changed rules” are that you’re referring to? As I said, I may be completely missing your point.