Mueller obviously thinks that Trump is guilty.
But that's just because he IS guilty.
I suppose you will say "you're rules!" and come up with some time when some Democrat obstructed justice, because that makes everything A-O-K in your mind.
I can promise you that if a Democratic president does stuff like this in the future, I will not cite Trump's precedent as an excuse, as if prior bad behavior justifies all future action. I can promise I will not lose my code of ethics.