I believe you can still be guilty of obstruction if you actively impede an investigation, regardless of its outcome.
That said, that the investigation resulted in no originating crimes being declared leaves the question of the validity and legality of the investigation in the first place. What was the probable cause? Isn’t this a “poisoned tree”? Why shouldn’t all of the indictments & convictions be thrown out? Lives were destroyed.
Mueller knew from the outset that there was no “Trump-Russia” activities, there was no evidence - so what about all the raids? Roger Stone was raided just weeks ago.
It all makes no sense UNLESS...the goal was ALWAYS to get PDJT on some form of “obstruction”. The investigation was just the vehicle to setup the right situation. Look at what they did, raiding his LAWYER - it was all to bait PDJT into some action that could be specifically pointed to. Their problem is that he didn’t do anything of significance that rises to the level of obstruction - this is what is driving them nuts. This is why the media is trying really hard to distort the “evidence” to reach the bar needed to claim impeachment justification, even to the point of just talking like it’s a no-brainer it does.
If they found some real crimes that would have just been a bonus, they probably thought they would find something - but if not the fallback was always obstruction.
...outside that, that the Mueller team was made up of purely Democrats, it might also have been to cover up the crimes of Hillary and Obama.
A president cannot “obstruct” his own branch of government. See post #16