Nobody said anything about a rule. The comment you initially responded mentioned a tradition. Those are two different things.
A tradition is where people were doing (or not doing, as in this case) something in the past, long enough and consistently enough that it become recognised as a thing.
During the 2016 campaign, one of the norms Trump was criticized, for breaking by both left and right was the norm that you don't prosecute your political opponents.[0][1] Specifically this was in the context of his campaign promise to "lock her up" ("her" being his opponent Hillary Clinton), a promise he didn't bother trying to keep while he was in office.
I don’t know that I agree with the whole narrative.
Nixon was pardoned, but the reason is that Nixon they were worried local and federal officials could act. I feel like that situation has it both ways. No tradition was protecting him so Ford acted.
Trump not prosecuting Clinton seems like it could just as easily be because they didn’t think they could get a conviction and frankly Trumps opinion on legal matters seems pretty random. I’m not sure that was out of any principle.
That’s almost certainly the case with Regan…I don’t know how you convict him.
I also don’t buy into this meaning the tradition would be absolute. If it was wouldn’t that encourage the worst behavior?