I never thought Clinton should have been impeached as it related to hiding a sexual affair. You expect people to lie about things like that. Congress should not have been involved. However, he stupidly testified and did lie to a grand jury and for that his license to practice law was revoked. Trump on the other hand never lied under oath. Refusing to testify is not a crime. The 5th Amendment allows us not to testify against ourselves. However, he did testify in the end and provided sworn statements regarding the collusion portion, the main thrust of the whole investigation for which there was no evidence of conspiracy. Invoking executive privilege is not a crime. Presidents do it all the time.
I agree, generally. That said, "Executive Privilege" isn't a "get out of jail free" card (no pun or point intended by use of that phrase), and as I mentioned earlier, Ken Starr asserted that claiming executive privilege was tantamount to obstructing justice or abuse of power, at least in some cases. There's a real, and larger question here about whether the President is above the law. Barr argues, essentially, that "if the President does it, it's not illegal." I have a problem with that, though I acknowledge the inherent problems, political and practical, of bringing a prosecution against a sitting president. I doubt there's an easy answer.
Regarding so called obstruction, they never had the evidence to prove that, so said Mueller, regardless of the OLR rules about not indicting a sitting president.
But remember that Mueller's job wasn't to prosecute Donald Trump, nor was it to prosecute or prove obstruction. Mueller's charge was to investigate Russian tampering, and in that process he laid out 10 instances where there was evidence of obstruction. The guidelines say you cannot indict the President, so, literally, no one who COULD prove obstruction with the evodebce provided is allowed to do so. So yes, no one "proved" Donald Trump is guilty of obstruction of justice, but that is *possibly* because no one is permitted to make that case.