Isn't it true that a client's communication to their attorney isn't privileged if they made it with the intention of committing or covering up a crime or fraud?
Yes, it's called, appropriately enough, the "crime/fraud exception." Admissibility usually depends on a judge's in camera review to make sure all the elements of the exception are present. The intent to commit crime or fraud has to be the client's intent, not the lawyer's. Generally that intent must be shown in the communication itself. So, if Rudy said "hey Trump, I just had a terrific week out there in Ukraine criming for you" and Trump says "Great!" that would not qualify as it does not show that Trump induced him to commit crimes, only that he approved of it after the fact.
I believe there is also an exclusion if the attorney is not acting primarily as an attorney but, for instance, as a shady political advisor.
It doesn't apply to anyone not acting as an attorney, but that's a tough one to prove.
Most of the evidence against Rudy isn't going to be in any of his communications with Trump anyway. However, tying it to Trump is where they will want to get into the communications. Because Trump will just say he was out criming for him without him knowing, just like Michael Cohen. Funny how many people are out there criming for Trump and he never knew about it. Didn't really even know any of the people who were doing it!