... and didn't anyone else here have a mother who would always respond with, "Two wrongs don't make a right," when you tried to deflect your bad behavior onto a sibling? My mom said it all the time, and it's as good a response as there is to people who think "what-about-isms" serve as a defense for misconduct.
I think the whataboutism in this context is "Looks like Santos should take a lashing for this... so who else that fits the bill should go down?".
If person X(D) and person Y(R) both do Z but only one (doesn't matter which) really takes any heat for it then it isn't the kind of whatabout like you posit. Under that scenario there isn't a whatabout regarding defense of action but rather the application of same standards. It's a legit observation. (And again it being a D or R shouldn't matter)