He probably shouldn't use words if you don't know what they mean. What about is him refers to excusing bad behavior because somebody else did some other Behavior which is perceived as bad.

When you're talking about the same behavior what you're talking about is precedent. And that is an entirely valid thing to talk about. President A did this, President B did this; now that President C is doing it, you really can't complain unless you also had a problem with President A and B doing it.

Whataboutism is something entirely different. Being wrong three times repetitively doesn't make it any better. Go back and try again